摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. TRANSACTIONS OF THE FARADAY SOCIETY Founded in 1903 to promote the study of Sciences lying between Chemistry Physics and Biology Volume 6 2 1966 Pages 1-1672 THE FARADAY SOCIETY LONDON 0 The Faraday Society and Contributors 1966 PRINTED IN GREAT BRITAIN AT THE UNIVERSITY PRESS ABERDEEN

ISSN:0014-7672    

DOI:10.1039/TF96662FP001

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. 118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions any particular point on the rigid surface becoming in turn negative neutral and positive these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. TRANSACTIONS OF THE FARADAY SOCIETY Founded in 1903 to promote the stdy of Sciences lying between Chemistry Physics and Biology Volume 6 2 1966 Pages 1673-3644 THE FARADAY SOCIETY LONDON @ The Faraday Society and Contributors 1966 PRINTED IN O W T BRITAIN AT TRE UNIVERSITY PRESS ABERDEEN

ISSN:0014-7672    

DOI:10.1039/TF96662FP003

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Absorption Spectrum of Triplet Benzene BY T. S. GODFREY AND G.PORTER Dept. of Chemistry, The University, Sheffield 10 Receiced 12th August, 1965 The absorption spectrum of triplet benzene has been observed by flash photolysis studies of benzene in rigid hydrocarbon glasses at 77°K. Although the triplet-triplet absorption spectra of many organic molecules have been observed by flash photolysis methods, attempts to detect the corresponding ab- sorption in benzene have hitherto been unsuccessful.1 The absorption of these triplet states has been invoked to interpret biphotonic processes which occur with benzene and its derivatives, particularly the sensitized decomposition of solvent at 77°K reported by Voevodsky and collaborators 2 and also the photo-ionization and thermoluminescence of benzene derivatives in hydrocarbon glasses2 These observations suggested that benzene should have an observable absorption in the region of 2537& in accordance with the theoretical prediction of Pariser.4 We have therefore re-investigated the flash photolysis of benzene, using low-temperature glasses in which the triplet lifetimes were known to be several seconds, and we have successfully recorded the benzene triplet absorption spectrum in the region expected. EXPERIMENTAL The general technique of low-temperature flash photolysis has been described pre- viously 5 but some modifications have recently been made. One of the main difficulties in previous work was the poor transparency of hydrocarbons at low wavelengths when frozen to a rigid glass.However, the following method of purification and drying of isopentane and 3-methylpentane 69 7 resulted in glasses which were transparent down to 225 mp in a 23 cm quartz cell.The hydrocarbon was treated with concentrated H2SO4 and con- centrated HNO:, for at least a week. (Small quantities should be used, especially if the starting material is not pure, and precautions should be taken against the possible risk of explosion.) It was washed with concentrated H2SO4 and then with water, dried with CaC12 followed by CaS04, refluxed over sodium overnight, passed through about 9 ft of activated silica gel and stored under vacuum. Immediately before use it was distilled on to a fresh sodium mirror and, from there, into a reservoir attached to the reaction cell. Benzene (B.D.H. “ for molecular weight determinations ” grade) was purified by vapour phase chromatography, weighed, dissolved in a little isopentane and then also distilled on to the sodium mirror.The solution was degassed by the usual freeze, pump, thaw, shake technique. When flashing, the reaction cell was held rigidly in the bottom of the Dewar by a seal of 50 % isopentane and 50 % 3-methylpentane. One of the benzene solutions flashed, containing 100 % 3-methylpentane as solvent, had to be cooled very slowly to prevent the hydrocarbon glass from cracking. This same solution also tended to crack when flashed with 900 J but was stable when only 225 J were used. However, most of this work was done with solvents containing about 65 ”/, isopentane and 35 % 3-methylpentane which could be cooled rapidly and flashed with 1000 J without cracking.All solutions were cooled for at least 30 min before flashing. The spectrum of triplet benzene was recorded on a photographic flash apparatus.8 This had two vertical flash lamps connected in series to condensers of 9pF capacity and 78 ABSORPTION SPECTRUM OF TRIPLET BENZENE charged to 15 kV. The analysis flash came from a horizontal capillary lamp and a shutter, opening 2 msec after the photolysis flash, cut out scattered light and fluorescence. A Joyce Loebl microdensitometer was used to trace the spectrum. T he kinetics of absorption and phosphorescence decay were measured on a photoelectric flash apparatus.9 Recently the zirconium arc monitoring source in this has been replaced by an iodine quartz lamp (Atlas A1/125, 12 V, 100 W) which emits down to about 220 mp, mwh lower than the zirconium arc.The apparatus also contained a grating mono- chromator and a R.C.A. 1P 28 photomultiplier. An Aminco-Kiers spectrophosphorimeter was used for some phosphorescence measurements. RESULTS ABSORPTION SPECTRUM OF TRIPLET BENZENE The spectrum was recorded photographically 5 msec after a 1.7 x 10-4 M solu- tion of benzene in 65 % isopentane and 35 % 3-methylpentane at 77°K had been flashed with lOOOJ, and was measured by comparison with the spectrum before flashing. In this way the hexatriene derivative, which is one of the products of benzene photolysis and absorbs in the same region as the triplet,lo had a negligible effect on the result. Neutral optical density rhodium filters were used for calibration of plate densities.I I I 220 2 be) 3 0 0 340 0.0 I wavelength (mp) FIG. 1 .-Triplet benzene absorption spectrum. The spectrum which is shown in fig. 1 has no structure and increases regularly in extinction from 340 mp to shorter wavelengths. Below 240 mp the photographic plate density is small and the optical density calibration is rather inaccurate so that the maximum shown at 240 mp cannot be regarded as established. No absorption could be detected when a solution of pure solvent (i.e., containing no benzene) was flashed. KINETICS OF ABSORPTION AND PHOSPHORESCENCE DECAY The kinetics of absorption decay were measured near 310 mp. Although the absorption here is not very intense, this wavelength was chosen to avoid the region of benzene phosphorescence (above 340 mp 11) and that of the hexatriene derivativeT .S . GODFREY A N D G . PORTER 9 absorption (below 290 mp 12). For this reason relatively high benzene concentra- tions (10-2 M) were used. Small changes in the wavelength around 310 mp had no effect on the decay rates, nor did changes in flash energy (1 10,225,900 or 1000 J). Good first-order plots were obtained from the decay curves and the half-lives, z, are given below. Phosphorescence decay rates were measured at 375 mp in the flash apparatus and also on a spectrophosphoriineter. The values obtained were identical within experimental error. Solution A : 8 x 10-3 M benzene in 58 % isopentane+42 % 3-methylpentane absorption z = 1.7+0.2 sec (average of 7 values), phosphorescence z = 2.0 0.2 sec (average of 12 values). Solution B : 10-2 M benzene in 100 % 3-methylpentane absorption z = 3.5 0-4 sec (average of 9 values), phosphorescence z = 3.9 & 0.3 sec (average of 9 values).The errors quoted are mean deviations from the mean. The reported lifetime of benzene phosphorescence in EPA glass is 7 sec 11 and we obtained the same value in this medium at 77°K. The more rapid decay in hydrocarbon glasses is attributed to their lower viscosity, the viscosity of solution A being 2.5 x 108 poise and that of solution €3 about 1012 poise.13 The reasons for the lifetime dependence on viscosity have been discussed 5 and will not be considered further since the sole purpose of our lifetime measurements was to establish the identity of the absorbing species with the phosphorescence emitter. ROOM-TEMPERATURE FLASH SPECTROSCOPY A solution containing lO-3M benzene in 100 % isopentane was flashed with 1000 J at room temperature and the spectrum recorded 12 psec and 55 psec after flashing.No transient absorption was observed below 290 mp, the region of triplet- triplet absorption, but there was a transient absorption at longer wavelengths which had a maximum at 324mp. This may have been a radical formed in some secondary reaction. The results were complicated by the presence of considerable fluorescence which could not, at the short delay times used, be eliminated by the use of a shutter. ESTIMATION OF EXTINCTION COEFFICIENT It is possible to estimate at least a lower limit for the extinction coefficient of the triplet absorption at various wavelengths and the absorption spectrum of the 1-7 x 10-4 M solution was used for this purpose. The optical density at any wave- length was obtained directly from the spectrum and the concentration was deduced from the singlet depletion.In benzene the three sharp singlet absorption bands (249, 255 and 261 mp) appear in the middle of the triplet absorption but a rough idea of the amount of depletion was obtained in the following way. At 249 mp, the peak of a singlet band, the optical density of the solution was 0-40. From the smoothed triplet spectrum, the optical density of the solution if it had contained the original concentration of benzene would have been 0.45 at this wavelength. There was therefore an apparent depletion corresponding to an optical density change of 0-05.However, as optical densities could only be measured to k0.02 and we were using the difference between two values, we can only conclude that the change in optical density was &0.05. The extinction coefficient of the 249 mp singlet band at 77°K was estimated to be 162 and allowing for a 20 % decrease in volume when the solution was cooled, the concentration change corresponding10 ABSORPTION SPECTRUM OF TRIPLET BENZENE to an optical density change of 0.05 is 1-3 x 10-5 M (i.e., 6+ 7:). At 240 mp the optical density of the triplet absorption was 0.5, the length of the reaction cell was 23.5 cm and therefore the extinction coefficient of the triplet is >1600. It is also interesting to calculate the triplet extinction coefficient at 2537& the wavelength of the mercury radiation frequently used for photolysis.A value of ~ > 1 3 5 0 was obtained whereas the singlet extinction coefficient at 77°K at this wavelength is only 53. DISCUSSION Our observation of triplet benzene absorption with a high extinction coefficient in the region of 2537A removes what has been a serious objection to the triplet absorption biphotonic mechanism. It is clear that in studies of benzene with mercury resonance radiation at low temperatures, when quite high stationary triplet con- centrations are possible, absorption by triplet state benzene will generally be a sig- nificant factor since the triplet extinction coefficient exceeds that of the singlet at this wavelength by a factor >20. As the triplet absorption band is such a wide one, and we may not yet have found its maximum, our limiting values for the extinction coefficient show that the transition we are observing is probably an allowed one.This agrees with Pariser’s theoretical prediction 4 that there will be a triplet-triplet absorption around 260 mp with an oscillator strength of 0.8. The failure of previous attempts to detect this spectrum is attributable to the experimental difficulties of flash photolysis in rigid glasses, the overlap of singlet and triplet absorptions and the uncharacteristic diffuse nature of the triplet spectrum. This diffuseness of the spectrum is not, however, unexpected since the triplet absorp- tion spectra even of naphthalene and anthracene are predissociated 14 and the total energy of the excited benzene triplet is greater still, being 8.5 eV for 2537 A absorp- tion, and 8-8 eV for 2400 A absorption, compared with a vapour phase ionization potential for benzene of 9.25 eV. We thank Dr. M. I. Savadatti for valuable discussions and help with experi- One of us (T. S. G.) also thanks I.C.I. for the award of a research mental technique. fellowship. 1 Porter and Windsor, Proc. Roy. Soc. A , 1958, 245,238. 2 Voevodsky, Vinogradova, Shelimov and Fok, Doklady Akad. Nauk., S.S.S.R., 1964,154, 188. 3 Gibbons, Porter and Savadatti, Nature, 1965, 206, 1355. 4 Pariser, J. Chem. Physics, 1956, 24, 250. 5 Hilpern, Porter and Stief, Proc. Roy. SOC. A , 1964, 277,437. 6 Potts, Jr., J. Chem. Physics, 1952, 20, 809. 7 Vinogradov, Can. J. Chem., 1962,40,2170. 8 Jackson and Porter, Proc. Roy. SOC. A , 1961, 260, 13. 9 Bridge and Porter, Proc. Roy. SOC. A , 1958, 244,276. 10 Anderton, Chilton and Porter, Proc. Chem. SOC., 1960, 352. 11 McClure, J. Chem. Physics, 1949, 17, 905. 12 Migirdicyan and Leach, J. Chim. Physique, 1961, 58, 409. 13 Lombardi, Raymonda and Albrecht, J. Chem. Physics, 1964, 40, 1153, 14 Porter and Wright, Trans. Faruduy SOC., 1955, 51, 1205.

ISSN:0014-7672    

DOI:10.1039/TF9666200007

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Deactivation of Excited Iodine Atoms I(52P*) BY R. J. DONOVAN AND D. HUSAIN Dept. of Physical Chemistry, University of Cambridge Received 9th June, 1965 Electronically excited (5p2P+) and ground state (5p2P*) iodine atoms, resulting from the flash photolysis of trifluoromethyl iodide, have been monitored in absorption in the vacuum ultra-violet region of the spectrum by the method of kinetic spectroscopy, A long-lived population inversion can be observed in the absence of laser action when argon is the added gas.Under these con- ditions, the rate of decay of I(52P+) is very slow so that deactivation by other added gases can be studied conveniently, particularly as the optical transition to the ground state is electric dipole forbidden. In argon the rate of decay of the excited iodine atoms increases with decreasing pres- sure although the absolute magnitude of the rate is some 5-6 times that calculated according to the Chapman-Enskog equation for the diffusion of xenon in argon.For N2 and C3Hs, the decay exhibits first-order kinetics for these gases and is independent of the pressure of added argon. No significant contribution to the removal of 1(52P+) by a hydrogen-atom abstraction reaction with propane was observed. No significant deactivation by CF31 itself was observed. The collision efficiencies for the deactivation of I(52P3) by the gases N2, C3Hs and I 2 (from a previous investiga- tion) are found to be 3-0 x 10-6, 3.2 x 10-4 and 7.2 x 10-2, respectively. ~ ~~ ~~ Kinetic studies of the deactivation of metastable, electronically excited, gaseous atoms have been carried out in a number of instances using flash photolysis with kinetic spectroscopy in absorption.Electronically excited mercury,1, 2 selenium 3 and iron49 5 atoms have been studied using this technique. More recently, the authors6 have observed excited (52P+) and ground state (52P3) iodine atoms pro- duced from the photolysis of molecular iodine and have monitored the decay of the electronically excited atoms. Deactivation of I(52P+) by I 2 proceeds at a rate of about one collision in 15. The high collision efficiency for deactivation by molecular iodine, together with the low yield of excited atoms on photolysis does not allow quenching by other gases to be studied conveniently. Work on atomic iodine photodissociation lasers by Kasper and Pimental 7 has shown that a population inversion for the two states (52P+ and 52P+) can be readily achieved by flash photolyzing gaseous methyl and trifluoromethyl iodides as evidenced by the resulting stimulated emission.A spectral analysis of ethyl iodide by Porret and Goodeve 8 had indicated that the photolysis of this compound should give rise to a high population of 1(5W+). Unfortunately, the atomic transi- tions most convenient for kinetic spectroscopy are obscured by the molecular spectrum of CH31. We have used CF31, generally in the presence of argon, under conditions which give rise to a population inversion without laser action, and have monitored the decay of the electronically excited atoms in the presence of various added gases. The determination of such collision efficiencies is clearly relevant to iodine atom chemistry studied by photolysis techniques and provides data necessary for a general consideration of electronic energy transfer.EXPERIMENTAL The experiniental arrangement for flash photolysis with kinetic spectroscopy in the vacuum ultra-violet was identical to that used by Donovan and Husain.6 A relatively low-energy spectroscopic flash source was triggered photoelectrically to take an absorption 1112 DEACTIVATION OF EXCITED IODINE ATOMS spectrum after the reactant system has been subjected to a high intensity flash of light.9 The time resolution was obtained by varying the electronic delay between the photolytic and spectroscopic flashes. It was therefore necessary 10 conduct a separate experiment for each time delay. The photolytic flash lamp which employed quartz molybdenum electrodes sealed in lead was U-shaped, of total length 67 cm, with a trigger electrode for initiation. The flash was obtained by discharging a bank of condensers of total capacity 8 pF (2x 4pF Wego low inductance, 20 kV rated condensers) at 16 kV (1024 J) through the lamp which contained 9.5 cm Hg of krypton and 5 mm of oxygen to prevent breakdown at lower volt- ages.The spectroscopic lamp was of thick-walled quartz capillary mounted inside a mechanical system employing suitably shaped hollow aluminium electrodes. The spectro- scopic flash was derived from the discharge of a low inductance condenser of capacity 1 pF (Dubilier) at 16 kV (128 J). The trigger circuit for this lamp, initiated by the delayed pulse, employed a 20 kV-rated deuterium-filled thyratron (English Electric Valve Co. CX 1140).The half-lives of the photolytic and spectroscopic flashes were 15 and 5 psec, respectively. The optical system was evacuated for vacuum ultra-violet spectroscopy. The units along the optical path comprised the spectroscopic lamp, an evacuated optical bench, a quartz reaction vessel and a bellows arrangement attached to the spectrograph. The evacuated optical bench consisted of essentially a brass rod carrying a lithium fluoride lens, focused for light of wavelength 1400 A. The reaction vessel was of length 30 cm, diam. 22mm with lithium fluoride windows (Harshaw Chemical Co.) sealed on each end with picene. To each unit along the optical path could be attached lithium fluoride windows held by mechanical O-ring seals. The bellows arrangement itself could carry a separate end-window enabling the spectrograph to be isolated.If necessary, each unit along the optical path could be pumped separately. In practice, to maximize light transmission, the only materials in the optical path were the end-windows of the reaction vessel and the lens. Observations were made with a 1 m grating spectrograph with a Rowland mounting of the type used by Thrush,lo maintained at a vacuum of 10-5 mm Hg, and spectra were recorded on Eastman S.W.R. film. The film was processed with Ilford contrast developer FF (diluted 1+9) for 3 min development time and plate intensities were measured with a Joyce-Loebel double-beam microdensitometer (Mark 11 1). We are indebted to Dr. M. J. Osborne for the preliminary construction of the apparatus.Plate intensities for the appropriate atomic absorptions of the ground and excited states were found to satisfy a Beer-Lambert type of relationship as indicated by the " two path " method so that intensity could be directly translated into relative concentration over a convenient range. The atomic transitions observed were : 1 (A) transition 1799 6~(2P*) c 5p(2P+) 1830 6~(4P+) c 5p(2P#). 1783 642P3)+5P(2P$ The lines at 1783 and 1799 A were used for photometry. All experiments were performed in the region of room temperature. The intensity of the molecular spectrum of iodine observed at the end of the reaction indicated that less than 8 % photolysis of CF31 had taken place and this, together with the small change in the spectral intensity in the vacuum u.-v.and the weak absorption spectrum in the region of quartz transmission,ll indicates that the temperature rise would only be 10-20 deg. Rate data are quoted for a temperature of 300°K. MATERIALS CF3I.-CF31 (Columbia Organic Chemicals Co.) was carefully degassed and frac- tionally distilled from a C02+ acetone slush (- 8S"C) to liquid-nitrogen temperatures. We are indebted to Dr. B. A. Thrush for a sample of this material. PRopAm.-Propane (99.99 mole %, Phillips Petroleum Co.) was carefully degassed and distilled from an n-pentane slush (- 140°C) to liquid-nitrogen temperatures.12 DEACTIVATION OF EXCITED IODINE ATOMS spectrum after the reactant system has been subjected to a high intensity flash of light.9 The time resolution was obtained by varying the electronic delay between the photolytic and spectroscopic flashes.It was therefore necessary 10 conduct a separate experiment for each time delay. The photolytic flash lamp which employed quartz molybdenum electrodes sealed in lead was U-shaped, of total length 67 cm, with a trigger electrode for initiation. The flash was obtained by discharging a bank of condensers of total capacity 8 pF (2x 4pF Wego low inductance, 20 kV rated condensers) at 16 kV (1024 J) through the lamp which contained 9.5 cm Hg of krypton and 5 mm of oxygen to prevent breakdown at lower volt- ages. The spectroscopic lamp was of thick-walled quartz capillary mounted inside a mechanical system employing suitably shaped hollow aluminium electrodes. The spectro- scopic flash was derived from the discharge of a low inductance condenser of capacity 1 pF (Dubilier) at 16 kV (128 J).The trigger circuit for this lamp, initiated by the delayed pulse, employed a 20 kV-rated deuterium-filled thyratron (English Electric Valve Co. CX 1140). The half-lives of the photolytic and spectroscopic flashes were 15 and 5 psec, respectively. The optical system was evacuated for vacuum ultra-violet spectroscopy. The units along the optical path comprised the spectroscopic lamp, an evacuated optical bench, a quartz reaction vessel and a bellows arrangement attached to the spectrograph. The evacuated optical bench consisted of essentially a brass rod carrying a lithium fluoride lens, focused for light of wavelength 1400 A. The reaction vessel was of length 30 cm, diam.22mm with lithium fluoride windows (Harshaw Chemical Co.) sealed on each end with picene. To each unit along the optical path could be attached lithium fluoride windows held by mechanical O-ring seals. The bellows arrangement itself could carry a separate end-window enabling the spectrograph to be isolated. If necessary, each unit along the optical path could be pumped separately. In practice, to maximize light transmission, the only materials in the optical path were the end-windows of the reaction vessel and the lens. Observations were made with a 1 m grating spectrograph with a Rowland mounting of the type used by Thrush,lo maintained at a vacuum of 10-5 mm Hg, and spectra were recorded on Eastman S.W.R. film. The film was processed with Ilford contrast developer FF (diluted 1+9) for 3 min development time and plate intensities were measured with a Joyce-Loebel double-beam microdensitometer (Mark 11 1).We are indebted to Dr. M. J. Osborne for the preliminary construction of the apparatus. Plate intensities for the appropriate atomic absorptions of the ground and excited states were found to satisfy a Beer-Lambert type of relationship as indicated by the " two path " method so that intensity could be directly translated into relative concentration over a convenient range. The atomic transitions observed were : 1 (A) transition 1799 6~(2P*) c 5p(2P+) 1830 6~(4P+) c 5p(2P#). 1783 642P3)+5P(2P$ The lines at 1783 and 1799 A were used for photometry. All experiments were performed in the region of room temperature. The intensity of the molecular spectrum of iodine observed at the end of the reaction indicated that less than 8 % photolysis of CF31 had taken place and this, together with the small change in the spectral intensity in the vacuum u.-v. and the weak absorption spectrum in the region of quartz transmission,ll indicates that the temperature rise would only be 10-20 deg.Rate data are quoted for a temperature of 300°K. MATERIALS CF3I.-CF31 (Columbia Organic Chemicals Co.) was carefully degassed and frac- tionally distilled from a C02+ acetone slush (- 8S"C) to liquid-nitrogen temperatures. We are indebted to Dr. B. A. Thrush for a sample of this material. PRopAm.-Propane (99.99 mole %, Phillips Petroleum Co.) was carefully degassed and distilled from an n-pentane slush (- 140°C) to liquid-nitrogen temperatures.R .J . DONOVAN AND D. HUSAIN 13 ARGoN.<ylinder argon (British Oxygen Co.) was purified by passage over P205, condensation at liquid-nitrogen temperatures followed by flash distillation. Spectro- scopically-pure bulb argon was used directly. NITROGEN.-NitrOgen (B.O.C. “white spot ”, 99.9 %) was bubbled through a column of amalgamated zinc in a 5 % solution of KOH saturated with sodium anthraquinone P-sulphonate, then through a column of amalgamated zinc in a solution of 0.1-0.5 N HCl containing 0.1 M CrC12 to remove 02, over a column of manganese sulphate between two columns of silica gel and finally through a trap at CO2+acetone temperature. RESULTS AND DISCUSSION DECAY OF I(52Q) IN ARGON Fig. 1 shows the production of I(52P4) and I(52P3) from the photolysis of CF3I in the presence of argon.A population inversion is observed with the almost com- plete absence of ground-state atoms and this inversion is long lived ( - 6 msec). The long life-time of the metastable excited atoms (5p2P4-+5p2P* (AE = -21.7 kcal) electric dipole forbidden) is illustrated in fig. 2. The decay of I(2P4) was found to r 0 B 0 .-.I I I I I I 1 I 1 I 1 1 2 3 4 5 6 7 8 9 10 II 12 17 time, msec FIG. 2.-Decay of I(52P4) in argon. e , PCF I = 0 5 mm ; PAr (spectroscopically pure) = 50 mm ; 0, PCF~I = 025 mm ; p k (spectroscopically pure) = 25 mm ; a, PCF~I = 0.5 mm ; p h (cylinder) = 50 mm. increase with decreasing pressure of argon and not to be significantly dependent on the pressure of CF31 as seen by the magnitudes of the rate coefficients in argon (fig.2 and table 1). The decay coefficients for the slow deactivation in spectroscopic- ally-pure argon are of limited accuracy. Further reductions in the pressure of inert gas to produce faster decay rates would result in a significant temperature rise on flashing, and reducing the partial pressure of CF3T itself below 0.25 mm did not allow the detection of excited atoms. It was therefore not possible to carry out quantitative measurements at lower pressures. A faster decay rate was ob- served if purified cylinder argon was substituted for spectroscopically-pure argon under otherwise identical conditions (fig. 2). Reducing the pressure of CF31 to one-half under these conditions did not significantly affect the decay rate (table 1) and it was concluded that impurities present in the cylinder argon, which we were unable to remove, were responsible for deactivation.Analysis of the “ purified ” argon using a Bendix time-of-flight mass spectrometer did not reveal significant amounts of impurity. The analysis did not allow the detection of oxygen or nitrogen14 DEACTIVATION OF EXCITED IODINE ATOMS in amounts less than 100 p.p.m. and such a level of oxygen impurity could possibly account for the observed decay rate, whilst nitrogen certainly could not. The deactivation of 1(52P+) by 0 2 was not measured on account of the strong Schumann- Runge absorption spectrum that would mask the atomic transitions and the com- plex chemical reactions that would result. Thus the long life-time of the excited TABLE RA RATE DATA FOR QUENCHING OF I(52P+) PCF31, mm Padded gas’ mm 0.5 025 0.5 0.25 050 0.5 0.5 0.5 0.5 *PI2 = 0.02 second-order unimolecular decay from ground state coefficient (ground constant k2 (cm3 calculated unimolecular growth quenching growth, ki (sec-1) ki (sec-l) molecules-1 sec-1) 24+4 (B = 5.54 sec-1) - - 60+ 10 (B = 11.08 sec-1) - - 1*4*01 X 102 - 1.2x 102 - 1-6h0.1 x 102 -1-2x102 - collision efficiency - - - - 2.8 X 10-6 3.1 X 10-6 3-2 x 10-4 3.1 x 10-4 3.1 x 10-4 0.072 0 2 (AZ) - - - - 1.2 x 10-5 1.3 x 10-5 4 2 x 10-3 +OX 10-3 +OX 10-3 0.581 * Donovan and Husain 6 t The decay coefficient obtained by direct measurement has been compared with that calculated from the gradient of the semi-logarithmic plot of the growth of the ground state versus time.0 @ e 0 - . 0 0 4-j- 0 0 I 2 3 4 5 6 7 8 9 1011 12 1 3 1 4 15 time, msec FIG. 3.-Growth of ground state iodine atoms. 0 , PCF,I = 0.5 mm ; (cylinder argon) = 50 mm ; 0, PCF~I = 0-25 mm; p k (cylinder argon) = 50 m iodine atoms for this particular group of experiments necessitates the use of argon of high purity. Experiments on the study of deactivation of 1(52P+) by other added gases were designed in order to make measurements in a time-scale during which diffusion and impurity quenching effects were negligible. The slow growth of the concentration of the ground-state atoms obtained by monitoring the absorption at 1783 A was difficult to measure for experiments em- ploying spectroscopically-pure argon. The growth rate for cylinder argon is in good agreement with the decay rates of the excited atoms (table 1).(S’ ince noR . J . DONOVAN AND D . HUSAIN 15 significant difference in the growth rates using two pressures of CF31 in cylinder argon could be detected, the results are presented on one curve with the logarithms of the plate densities of one set of measurements suitably displaced.) The measurements of atomic concentrations presented here are not absolute. We intend to attempt an absolute measurement at a later stage by thermal calibration of the ground-state absorption intensity.6 The growth rate of the ground-state falls at somewhat longer times. This is possibly due to recombination of ground- state atoms to molecular iodine whose intense absorption spectrum is only observed at long delay (fig.1) and the loss of ground-state atoms at the wall of the vessel. There is no recombination by two 1(2P+) atoms as these give rise to a repulsive state 12 and also, no significant effect of the process I(52P+)+I(52P+)+ M+12(B311&,)+M as seen by the reasonably good first-order decay of I(52P4). Methyl radicals observed on flashing methyl iodide 13 under similar conditions to those described for CF31 were short lived ( N 100 psec) and it may be concluded that CF3 radicals experience a similarly short life and do not affect the removal of I(52P+) at longer time delays. DIFFUSION AND SPONTANEOUS EMISSION OF I(52Pa) The rate of decay of I(2P+) in argon can be roughly compared with that expected If removal is by diffusion only, the rate equation can be on the basis of diffusion.written : where D is the diffusion coefficient at the appropriate pressure. length I and radius I", the solution tends to the form 14 : v2 [I(~P+)-~ = ( i o)a [I(~PJJI~ t , For a cylinder of p = ($+?)D. The binary diffusion coefficient for a xenon + argon mixture was calculated using the empirical '' combining laws " for the Lennard-Jones parameters for xenon and argon, and the " first approximation " Chapman-Enskog equation.15 A comparison of the calculated values of p with the observed decay rates shows the latter to be about 5-6 times as fast as the diffusion of xenon in argon (table 1). The rate, however, does increase by a factor of 2-5 on halving the inert-ga! pressure. A factor of 2 would be expected for a diffusion-controlled process.A qualitative consideration of the expected Lennard-Jones parameters for an I(2P4) + Ar mixture might lead one to expect a slower rate of diffusion. If the non-diffusional contribu- tion to the decay derives from CF31 itself, this would represent a deactivation probability roughly in the range 1-7 x 10-5. A further possibility is chemical reaction according to the process If the value for D(CF3-I) is taken to be 28+5 kca1,16-18 this reaction is 29 kcal exothermic. A higher value of 57+4 kcal quoted by Mortimer 19 leads to an exothermicity of 1 kcal. A similar reaction has been postulated by Myer 20 to ac- count for the fast production of 12 observed in time-resolved mass-spectrometric studies on CH31. With CF31 in these experiments, molecular iodine is only detected at long delay and thus any contribution by the proposed reaction must be negligibly small, favouring the higher value for D(CF3--I).On the other hand, if the excess rate above that calculated for diffusion is the result of spontaneous emission for the transition 1(52P+) iI(52P3.) + hv, our data would suggest a mean radiative life-time C F31 +- 1( 52P4) ->CIF3 + 12.16 DEACTIVATION OF EXCITED IODINE ATOMS lying between 0-02 and 0.05 sec. Garstang 21 has calculated this to be 0.13 sec. However, the increasing rate on decreasing the total pressure indicates that diffusion predominates over spontaneous emission. QUENCHING BY NITROGEN AND PROPANE The quenching of I(52P4) by nitrogen was studied under conditions of pressure which resulted in a negligible contribution by diffusion to the decay rate (fig.4). The decay satisfied first-order kinetics with respect to the concentrations of both nitrogen and electronically excited iodine atoms (table 1) and was found to be rela- tively slow with a collision efficiency of about 3 x 10-6. Quenching by propane was more efficient by about a factor of 100 (fig. 4, table 1) and thus only a relatively small pressure was required to yield a decay rate that could be studied in a convenient 0.8 0 . 5 1.0 1.5 time, msec FIG. 4.-Deactivation of I(52P+) by nitrogen and propane. 0, ~ C F ~ I = 0.5 llltn ; p~~ = 100 llltn 0, PCF3I = 0.5 mm ; ~ c ~ H ~ = 1.25 mm ; p k = 48 mm 0, PCF3I = 0.5 mm; ~ c ~ H ~ = 1.25 D; PAr = 98 mm time range. It was therefore necessary to add an excess of argon to pressure-broaden the appropriate atomic transitions sufficiently in order to monitor the atomic con- centrations by plate photometry.The decay rate of I(52P+) was first order with respect to 1(52P+) itself and to propane and zero order with respect to argon. The growth of the ground-state atoms was equal to the rate of decay of the excited atoms, within experimental error (table l), thus indicating that the removal of I(52Pd occurs primarily by spin-orbit relaxation rather than by a hydrogen-atom abstraction reaction with propane. Furthermore, hydrogen iodide was not de- tected during the period of deactivation in spite of its strong absorption spectrum in this region9 Deactivation of I(52P4) by the gases N2, C3Hg and 12 yield collision efficiencies varying over a range of about 2 x 104.No simple correlation between collision efficiency and any parameter of the deactivating molecule has been found. The efficiency does increase with decreasing ionization potential for the three gases mentioned 2 3 which suggests a relatively strong attractive interaction, not necessarily of the charge-transfer type, on collision. The high quenching efficiency of mole- cular iodine itself is presumably the result of the production of a relatively stableR. J . DONOVAN AND D . HUSAIN 17 1 3 complex. The rough correlation with ionization potential does not apply to CF3I24 and Ar. The extremely low efficiency of quenching of 1(52P+) by argon appears (since it was not quantitatively determined) to be in accordance with Callear’s 25 diagram for the interconversion of electronic and translational energy, on which the data conform roughly with the general law where P is the probability of quenching, AE is the energy converted to translation and where for this class of energy transfer system, A is a constant and B can be neglected.Essentially two general explanations can be presented to account for the observations. Callear 2, 25 has reviewed the experimental data on the deactiva- tion of electronically excited atoms by polyatomic molecules and concludes that the rate of collisional deactivation is not determined by optical metastability, and that for all known examples, energy transfer occurs at short range and results from the near-crossing of non-parallel surfaces. An alternative theory for the deactiva- tion of electronically excited iodine atoms is that suggested for Hg(63P1) by Bykhovskii and Nikitin 26 involving the loss of degeneracy on cgllision.1(52P+) and I(52P%) would give rise to 2 and 4 states respectively, under the influence of the electric field due to the colliding molecule and thus the large number of potential surfaces would facilitate crossing. logP = -AAE+B, The authors thank Prof. R. G. W. Norrish, F.R.S., for encouragement and laboratory facilities, and Dr. A. B. Callear for helpful discussion. One of us (R. J. D.) is indebted to the Department of Scientific and Industrial Research for a main- tenance grant during the tenure of which this work was carried out. 1 Callear and Norrish, Proc. Roy. SOC. A, 1962,266,299.5 2 Callear and Williams, Trans. Farday SOC., 1964, 60, 218. 3 Callear and Tyerman, Nature, 1964,202, 1326. 4 Thrush, Nature, 1956, 176, 155. 5 Callear and Oldman, private communication. 6Donovan and Husain, Nature, 1965,206, 171. 7 Kasper and Pimental, Appl. Physics Letters, 1964, 5, 231. 8 Porret and Goodeve, Proc. Roy. SOC. A, 1938,165, 31. 9 Norrish, Porter and Thrush, Proc. Roy. SOC. A, 1953,216, 165. 10 Thrush, Proc. Roy. SOC. A , 1956,243, 555. 11 Hazeldine, J. Chem. SOC., 1953, 1764. 12 Mathieson and Rees, J. Chem. Physics, 1956, 25, 753. 13 Herzberg and Shoosmith, Can. J. Physics, 1956, 34, 523. 14 Mitchell and Zemansky, Resonance Radiation and Excited Atoms (Cambridge University Press, 15 Hirschfelder, Curtis and Bird, Molecular Theory of Gases and Liquids (Wiley, New York, 16 Mariott, Thesis (University of Liverpool, 1954). 17 Craggs and McDowell, Reports Progr. Physics, 1955, 18, 374. 18 Stacey, Tatlow and Sharp, Advances in Fluorine Chemistry (Butterwroths, London, 1963), 19 Mortimer, Reaction Heats and Bond Strengths (Pergamon, London, 1962), p. 134. 20 Meyer, private communication to R. G. W. Norrish, University of Cambridge. 21 Garstang, J . Res. Nut. Bur. Stand. A, 1964, 68, 61. 22 Price, Proc. Roy. SOC. A, 1938, 167, 216. 23 Field and Franklin, Electron Impact Phenomena and the Properties of Gaseous Ions (Academic 24 Price and Ridley, unpublished data in Advances in Fhorine Chemistry, Stacey, Tatlow and 25 Callear, Applied Optics, 1965, Suppl. 2 Chemical Lasers, p. 145. 26 Bykhovskii and Nikitin, Optics Spectr., 1964, 16, 11 1 (201). 1934,), p. 247. 1954), p. 539, 567, 1110. vol. 2, p. 17. Press, New York, 1957). Sharp (Butterworths, London, 1963), vol. 2, p. 65.

ISSN:0014-7672    

DOI:10.1039/TF9666200011

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No.13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Charge-Transfer Complexes of some 5-Membered Heterocyclics and their Annellated Derivatives with Tetracyanoethylene BY A. R. COOPER, C . W. P. CROWNE AND P. G. FARRELL Dept. of Chemistry, Sir John Cass College, London, E.C.3 Received 12th July, 1965 The electronic spectra and association constants for the interactions between a series of 5-mem- bered ring donors and tetracyanoethylene (TCNE) have been measured.Together with the enthalpy and entropy changes found for the furan-TCNE and thiophen-TCNE interactions the results indicate charge-transfer complex formation in these systems. The spectra have been correlated with the calculated highest-occupied orbital energies of the donor molecules and used to obtain ionization potentials for these molecules. The results indicate that these molecules are n-electron donors. The formation of charge-transfer complexes between non-alternant hetero- cyclic or homocyclic electron donors and electron acceptors has been investigated in only a few cases.1-3 In particular, Lepley has shown that fluorene and related molecules act as donors towards 2,4,7-trinitrofluorenone,z Lang has studied the iodine complexes of a number of heterocyclic donors 3 and Foster and Hanson have reported their work on complexes of indole with TCNEM and both indole and substituted indoles with chloranil.4b This recent work prompts us to report our investigations of the TCNE complexes of 5-membered ring donors containing various hetero-atoms (including indole).Association constants for these systems in chloroform solution have been measured at their wavelengths of maximum absorption. The free energies of forma- tion calculated from these constants at these wavelengths (8% 103-104) support the theory of charge-transfer complex formation. The effects of linear annellation and of varying the heteroatom upon both the association constant and the charge- transfer absorption maximum have been studied, and comparisons drawn between these non-alternant donors and a number of alternant-hydrocarbon " model " donors also studied.Enthalpy and entropy changes on complex formation have been measured for the furan and thiophen complexes from the variation of their association constants with temperature and shown to be small. The values obtained are in agreement with those expected for weak intermolecular charge-transfer interactions. Several workers have shown that, to a first approximation, the energies of these charge-transfer bands should be simply related to the energies of the highest-occupied molecular orbitals of the donor molecuIes.1~1 29 5 Molecular orbital calculations have been carried out on these heterocyclic donors, and on a number of model alteraant hydrocarbons for comparison, to obtain values for the energy (in units of the carbon-carbon resonance integral p) of their molecular orbitals in order to examine this relationship for non-alternant donors.The parameters used and the results obtained are discussed, and these results used to predict values for the highest- occupied orbitals of some non-alternant hydrocarbons from their charge-transfer spectra with TCNE. A8A. R. COOPER, C . W. P . CROWNE AND P . G. FARRELL 19 Values for the ionization potentials of the donors may also be obtained from charge-transfer spectra and different workers have proposed expressions relating the energy of the charge-transfer transition with various acceptors to the donor ionization potential.6 An expression deduced previously by one of us for TCNE complexes 7 has been used to predict ionization potentials for these heterocyclic donors, and these values are discussed in the light of measured values where available.EXPERIMENTAL MATERIALS ELECTRON DONORS.-with the exception of benzofuran all the donors used were com- mercial products which were either recrystallized to constant melting point, or redistilled and collected at their boiling points. Benzofuran was prepared from commercially obtained coumarin. Bromination of coumarin yielded coumarin dibromide,s which on treatment with alcoholic potassium hydroxide gave coumarilic acid. Decarboxylation of this to benzofuran was effected by heating with copper powder in quinoline,g b.p. 171". TETRACYAN0ETHYLENE.-This was obtained commercially, recrystallized from chloro- benzene, and sublimed twice at 125"/4 mm, m.p.197-199" (sealed tube) (lit.10 198-200"). treatment. SoLVE"r.-The values of the association constants for polycyanobenzene complexes measured in both alcohol-free chloroform and in A.R. chloroform containing approxim- ately 1 % ethanol as stabilizer were identical within the experimental error.11 We have not found this to be true for TCNE complexes and in order to ensure reproducibility of results chloroform containing 2 % by volume of ethanol was prepared from A.R. chloroform. The ethanol in commercial A.R. chloroform was first removed by treatment with con- centrated sulphuric acid.12 After washing with distilled water, drying and redistilling, 2 % by volume of dry ethanol 13 as stabilizer was added. 7,7,8,8-TETRACYANOQUINODIMETHANE.-A pure sample was used without further MEASUREMENTS The new charge-transfer bands which appear when the donors are dissolved with TCNE in chloroform were recorded using a Beckman DK2 spectrophotometer fitted with a constant-temperature cell-housing thermostatted at 24 30.2". Solutions of the complexes were prepared in 10 mm stoppered silica cells immediately before use, the donor con- centration being adjusted to give between 45 and 75 % absorption for the complex.Each spectrum was run at least three times. Assuming that the intensity of this absorption measures the total concentration of the 1 : 1 charge-transfer complex AD, formed between the donor D and the acceptor A, we have evaluated the association constants and extinction coefficients at the wavelengths of maximum absorption of the complexes in table 1 by the Benesi-Hildebrand method,l4 using molar concentrations throughout. Optical density measurements of solutions con- taining a constant concentration of TCNE and varying excess donor concentrations were made at 22f0.2" using a Unicam SP500 manual spectrophotometer fitted with a thermo- statted cell-housing. All measurements were made immediately after mixing the com- ponents, the same 10 mm matched silica cells being used throughout.In all cases linear plots of [TCNE] LID against the reciprocal of the donor concentration were obtained ([TCNE] = concentration of TCNE; L = path length of cell; D = optical density of the solution at the wavelength of measurement for the complex in a cell of path length L).Numerical values of the slope and intercept were calculated by the method of least squares. Pyrrole, indole and phenanthrene exhibit charge transfer absorption which decays slowly during the time required for the optical density measurements necessary for the evaluation of the association constants, further absorption bands appearing in the spectra20 CHARGE-TRANSFER COMPLEXES of these systems due to the formation of substitution products.15 The rate of this reaction with pyrrole was too rapid to obtain reproducible association constants for this complex, but a reliable absorption maximum was obtained at low temperatures (ca. -40") using a vacuum-jacketed cell. Reproducible results were obtained for the association constants of the indole and phenanthrene complexes by following the decay of the optical density due to the complex with time for various concentrations of the complex.This rate of decay was first-order with respect to the complex and extrapolation to zero time of the TABLE VALUES OF THE ASSOCIATION CONSTANTS K AND WAVELENGTHS OF ABSORPTION ACT FOR THE CHARGE-TRANSFER COMPLEXES FORMED BETWEEN TCNE AND VARIOUS DONORS IN CHLOROFORM I II I11 IV V VI VII VIII IX X XI XI1 XIII XIV xv XVI XVII donor dibenzofuran dibenzothiophen carbazole phenanthrene C fluorene d diphenyl d benzo furan benzo[b] thiophen indole c naphthalene d indene styrene furan thiophen benzene d pyrrole c butadiene C 'CT (mP) 498 550 605 535 567,419 505 465 528,477 543 550,430 542,430 485 450 399 39 1 530 425 AT 22" K 4 &a, b - AG - AH - TAS (1.mole-') (1. mole-1 cm-1) (k=l) (kcal) (kcal) 1 -05 f 0.04 1650 0-03 10.02 1-33 50.04 3350 0.17 50.02 5-12f0.13 2900 0-96 10.02 1-99i-0-12 1750 040 f 0.04 1.44f0.08 2000 0.21 i0 03 0.73f0.02 1050 -019f0 01 1.0710.04 1100 0.04f0 02 1 a08 f 0-03 1700 0.04f0 02 4.8 f0.2 3000 0.92-fOO3 1*0110*04 1600 0.01 f0.02 1.63f0.04 1350 0.29 f0.02 0.65f0.01 1250 -0.25f0.01 0.29f0.02 1100 -0.73f0.05 2.0 2.7 0.48f0.02 1450 -0*43f0*02 2.6 3.1 0.25f0.01 2900 -0.80f0.02 e (a) mean values of three or more determinations measured at the wavelength of maximum (b) &50 1. mole-1 cm-1. (c) Absorption due to the complex decays slowly owing to the formation of substitution products. (d) previously recorded values in dichloromethane at 22" (Merrifield and Phillips, J.Amer. Chern. SOC., 1958, 80, 2778) expressed in mole fraction units : fluorene K = 18.0, E = 1430; diphenyl K = 4.09, E = 1450 ; naphthalene K = 11-7, E = 1240 ; benzene K = 2-00, E = 3570. (e) value obtained in dichloromethaned -AH = 2 3 kcal. absorption of the complex, with the exception of benzo[b]thiophen (measured at 528 mp). linear plot of the logarithm of the optical density against time gave the initial optical densities. These latter values were used to calculate association constants and extinction coefficients for these complexes (table I). Enthalpies of formation for the furan and thiophen complexes were obtained from a van't Hoff equation plot. Measurements of the optical densities of solutions containing known donor and acceptor concentrations were made at various temperatutes and the association constants for these temperatures cal- culated directly using the values of the extinction coefficients for the complexes obtained at 22'.It was assumed that these extinction coefficients were temperature independent.16 RESULTS AND DISCUSSION SPECTRA The spectra of solutions of TCNE with various donors in chloroform show an extra absorption band not due to either component alone and in a few cases two extra bands are observed (see table 1). These bands have been attributed to the formation of donor-acceptor complexes in these solutions. This assignmentA. R. COOPER, C. W. P. CROWNE AND P. G. FARRELL 21 is supported by the linear relationship between the frequencies of the long wave- length maxima for these complexes and the frequencies of the maxima for the com- plexes of the same series of donors with another acceptor (see fig.I), this relation- ship having been generally observed.4bs 11917 Taking the long wavelength absorp- tion band of the complex as a measure of the acceptor strength, for this series of donors 7,7,8,8-tetracyanoquinodimethane is a slightly stronger acceptor than TCNE on average. 8 - 8 2.: E 3 a "8 /v 3 XI V d f I/ /.5 2.0 2 -5 3.0 ~ V C T 7,7,8,8-tetracyanoquinodimethane complexes (ev) FIG. 1 .-Plot of ~ V C T for complexes of 7,7,8,8-tetracyanoquinodimethane with various donors against ~ V C T for the corresponding TCNE complexes in chloroform at 22". The numbering is as in table 1 ; XVIII = anthracene ; XIX = 11 H-benzo[a]fluorene ; XX = 11 H-benzo[b]fluorene ; XXI = 7 H-benzo[c]fluorene. With the exception of furan, the charge-transfer maxima for the oxygen com- pounds are at shorter wavelengths than those for the corresponding nitrogen and sulphur analogues, as is to be expected from the greater electronegativity of the oxygen atom.The TCNE complex with furan absorbs at a slightly longer wave- length than that with butadiene in accordance with the observations that cis-dienes themselves absorb at longer wavelengths than trans-dienes, as exemplified by cyclo- pentadiene and butadiene.18 However, no charge-transfer maximum could be observed in either chloroform or tetrahydrofuran solutions of cyclopentadiene and TCNE, although the occurrence of a yellow colour on mixing in the latter solvent has been reported.19 (TCNE alone in tetrahydrofuran gives a yellow solution due to the formation of a charge-transfer complex.lb) The complexes of the other oxygen donors absorb at similar wavelengths to those of the corresponding alter- nant hydrocarbons formed by loss of the oxygen atom (see table I), suggesting that there is little delocalization of the oxygen lone-pair electrons.Models indicate that the constraining effect of introducing a bridge oxygen into diphenyl is less than it is in the other model compounds, butadiene and styrene, and the values of the charge-transfer maxima for diphenyl and dibenzofuran support this.22 CHARGE-TRANSFER COMPLEXES The sulphur-containing donors form complexes whose maxima are close to those of the corresponding hydrocarbon complexes as expected (cf.dibenzothiophene and phenanthrene, etc.), whereas the complexes with the nitrogen compounds absorb at longer wavelengths than either their sulphur or oxygen analogues. This may be due to the greater conjugation of the nitrogen lone pair electrons with the conjugated systems, or to some more specific interaction with the nitrogen atom as in the N-tricyanovinylation of aniliiies.20 However, the latter seems unlikely as the substitution products of the reactions of pyrrole and indole with TCNE are 2-tricyanovinylpyrrole and 3-tricyanovinylindole respectively.15 ENTHALPIES The weak intermolecular charge-transfer complexes formed between electron donors and various electron acceptors generally have free energies of formation of a few kcal/mole and negative enthalpy factors.21 From the variation with temperature of the association constants of the TCNE complexes with furan and thiophen, the enthalpies of formation for these complexes have been found to be respectively - 2.0 kcal mole-1 and - 2.6 kcal mole-1.These values are lower than those for aromatic hydrocarbon-TCNE complexes,21 but are close to the value for the indole-TCNE complex (- 3.08 kcal mole-l).4a ASSOCIATION CONSTANTS Values of the association constants for the complexes, together with the wave- lengths of maximum absorption at which they were measured and the extinction coefficients at these wavelengths are shown in table 1. With the exception of the nitrogen compounds, all the association constants are comparable in magnitude and give free energies of formation of only a few 100 cal/mole.Indole and carb- azole form stronger complexes with TCNE, the association constants for these being of similar magnitude to those for alkylaniline-TCNE complexes.22 No repro- ducible value for the pyrrole-TCNE complex at 22" could be obtained owing to the rate of the further reaction. TCNE is a more powerful electron acceptor than chloranil6b and should form the stronger complex with a given donor. This may be seen from a comparison of the association constant values at 22" for the indole-TCNE complex in chloroform (4.8 1. mole-1) and for the indole-chloranil complex in carbon tetrachloride (2.72 1. mole-1). (Foster and Manson report a value of 2-93 1.mole-1 for the indole- TCNE complex in dichloromethane at 22".4a) It may be assumed that the associ- ation constant for the indole-chloranil complex in chloroform would be lower than the value obtained in carbon tetrachloride as solvent. Association constants for the furan and thiophen complexes with TCNE are considerably lower than those for the bi- and tri-cyclic molecules. This may be due to the greater " effective electronegativity " of the heteroatom in a monocyclic 5-membered ring system as compared with the bi- and tri-cyclic systems thus making the monocyclics weaker donors, notwithstanding the fact that they have an average of 1.2 .n-electrons per atom and should therefore be strong donors. However, the benzene-TCNE complex also has a low association constant (0.25 1.mole-1) sug- gesting that the " strength " of these complexes as reflected by their association constants may be a function of the size and hence the degree of orbital overlap with TCNE of these planar donor molecules. The association constants obtained for the complexes with the homocyclic non- alternant donors, together with their wavelengths of absorption, suggest that thereA . R . COOPER, C . W . P . CROWNE AND P . G . FARRELL 23 is greater overall n-electron conjugation in these molecules than in the corresponding oxygen heterocyclics, implying a considerable degree of hyperconjugative electron release from the CX2 group. It has also been suggested that the polynitroaromatic compounds function most effectively as acceptors towards aromatic hydrocarbons only when the donor is sufficiently large to overlap the entire acceptor molecule,23 and our results are in general agreement with this for these donors.ENERGY LEVELS The energy of the new absorption band occurring in the electronic spectra of solutions containing an electron donor and an electron acceptor, due to the formation of a charge-transfer complex, may be expressed as where ECT = energy of the charge-transfer absorption band, A, the energy of the lowest-unoccupied molecular orbital of the acceptor molecule, Di the energy of the highest-occupied molecular orbital of the donor molecule.* For the complexes formed by a number of donors with a given acceptor under identical conditions, there should be a linear relationship la, 2, 5 between the energy of the long-wavelength charge-transfer band and the energy of the highest-occupied molecular orbital of the donor.For conjugated molecules, orbital energies may be expressed in the form where o! = coulomb integral for carbon, /? = carbon-carbon resonance integral, xi = calculated parameter for the ith molecular orbital of the donor (and similarly for q), cc and /? being assumed constant. We have calculated the orbital energies of these 5-membered ring donors using the simple Hiickel method with neglect of overlap,24 incorporating the heteroatoms by use of the relationships (3) and (4), ECT = hVCT = Aj Di, (1) Di = CC+X&~, Dj = u-xJI (2) a, = a + h,P, (3) locx = kxP7 (4) where EX = coulomb integral for the heteroatom X, /ICX = resonance integral for the carbon-heteroatom bond, hx and kcx are chosen parameters for the hetero- atom X.25 The choice of hx and kcx is shown in table 2 and the results of the calculations, together with the energies of the long-wavelength absorption bands for the charge-transfer complexes of these 5-membered ring donors with TCNE are shown in table 3.Also included are data for a number of model alternant n-electron donors. Calculations on the sulphur-containing donors were carried out by both the simple Huckel method and by the method of Longuet-Higgins,26 using the parameters given at the end of table 2 in this second method. The similarity in the positions of the charge-transfer maxima for the TCNE complexes formed by these donors to those for the complexes of the corresponding benzenoid donors suggests that the energy levels of the highest-occupied molecular orbitals in the two series of corn- pounds are similar in magnitude (cf.thiophen and benzene, benzo [blthiophen and naphthalene, dibenzothiophen and phenanthrene). As seen from table 3 this similarity is reproduced by the calculations involving the &orbitals of the sulphur atom, whereas the results obtained by the Huckel method are neither consistent with the charge-transfer spectra nor with the experimentally measured ionization potential of thiophen.27 * Throughout this paper the subscript i refers to a highest-occupied molecular orbital and the subscript j to a lowest-unoccupied molecular orbital.24 CHARGE-TRANSFER COMPLEXES The relationship between ~ V C T and xg is shown in fig.2 where a fair linear rela- tionship obtains which would no doubt be improved by more refined calculations. The effect of the inclusion of the model alternant compounds (except butadiene) upon the slope of this relationship is to increase it slightly (see fig. 2). This small TABLE 2.-PARAMETERS heteroatom X .. -0- -N- .. I .. -S- .. -S- USED FOR THE CALCULATION OF THE ENERGY LEVELS OF 5-MEMBERED HETEROCYCLIC MOLECULES hX kCX 2.0 0.8 1.0 0.9 0 0 0.6 TABLE 3.-cHARGE-TRANSFER ENERGIES MEASURED IN CHLOROFORM AT 24" FOR THE COMPLEXES FORMED BY VARIOUS DONORS WITH TCNE, TOGETHER WITH THE HIGHEST-OCCUPIED MOLECULAR ORBITAL PARAMETERS AND IONIZATION POTENTIALS FOR I I1 I11 IV V VI VII VIII IX X XI XI1 XI11 XIV xv XVI XVII XVIII XIX xx XXI donor di benzofuran dibenzothiophen carbazole phenanthrene anthracene benzofuran benzo[b]thiophen indole naphthalene styrene diphenyl furan thiophen pyrrole benzene butadiene fluorene indene 1 1 H-benzo [alfluorene 1 1H-benzo[b]fluorene 7H-benzo[c]fluorene h"CT (eV) 249 226 2-05 2-32 1.77 2.67 2.35 2.29 2.26 2.56 2.46 2.76 3.11 2.34 3.23 2.92 2.19 2-29 1.87 1-95 1.84 THESE DONORS Xf 0.705 0.664,e 0.705 054 0.605 0.414 0.62 1 0.646,s 0.192 0.534 0618 0.662 0.705 0.618 0.875,.0369 0.618 1 .Ooo 0.618 0.587,l 0.576 m 0*613,1 0600 m 0*502,1 0.497 m 0.525,r 0.519 0494,l 0.490 m S I X 4 + xj 0.48 0.50 0-4 1 050 0.50 0.43 0.50 0.38 0.50 0.50 0.50 0-39 0.50 0.34 050 0.50 h v (eV) 4-97 b 4.36 b 427 b 4-24 9 3.31 0 5.09 b 483 b 4.76 b 4.36 9 5-09 f 4.91 6-00 9 476 g 3.93 n 3.91 n 3.83 n ID" (eV) 8.26 7.97 7-72 8-05 7.38 8.47 8.09 8-01 7-97 8.34 8.22 8.58 9.00 8.08 9.16 8.78 7.89 8.01 7.50 7.60 7-46 ID (other workers) (eV) 8.59,c 8.58 d 8.15 d 8.09 a 8.50,c 8-07,d 8.62 h 8.1 1 ,C 7.42,d 8.20 h 8.67.c 8.66 d 8.48 d 8.43 d 8.63,e 8-15.d 8-12,4 8.68 h 8.66,d 8-46 f 8*79c, 8- 53 ,d 8.27 f 8.93.c 8.89,f 9.01 k 8.91 * 8.61,~ 8-20,; 8.90 * 9.53.c 9.30.d 9.245.f 9.52 h 9.07 8 .5 6 , ~ 8.43 d 8.63 c 8-55 d 8.54 d 8.48 d (a) calc. from eqn. (8) ; (b) Badger and Christie, J. Clzem. SOC., 1956, 3438 ; (c) ref. (29) ; (d) calc. from the p band transitions of the donor molecules using the expression proposed by Kuroda, Nnture, 1964, 201, 1214; (e) calc. by the method of Longuet-Higgins 26 ; (f) calc. by the simple Hiickel method 24 ; (8) Clar, Aromatische Kohlenwusserstofe.(Springer-Verlag, 1952) ; (h) electron-impact value quoted by Streitwieser 25 ; ( i ) photo-ionization values 31-33 ; 0') Rao, Ultra-Violet and Visible Spectroscopy (Butterworths, 1961) ; (k) Spectroscopic values, Price and Walsh Proc. Roy. SOC. A, 1941,179.201 ; ( I ) taken from fig. 2A; (m) taken from fig. 2B ; (n) Clemo and Felton, J. Chem. SOC., 1952, 1659. increase suggests that the parameters chosen for the heteroatoms accord with the heterocyclic molecules being analogous to the benzenoid systems, i.e., that the electron transfer takes place from the n-electron system of the donor, and also with the conclusions of Lang from studies of the iodine complexes of thiophen, 2-methyl- furan and N-methylpyrrole.3A. R. COOPER, C.W. P . CROWNE AND P . G. FARRELL 25 The oxygen-containing donors differ considerably from the other heterocyclics in that they are more closely related, both in orbital energy and charge-transfer maximum, to the alternant hydrocarbon containing only their n-electron system, i .e., furan and butadiene, benzofuran and styrene, dibenzofuran and diphenyl. This accords with there being little delocalization of the lone-pair electrons of the oxygen atom. From fig. 2 and their observed charge-transfer maxima with TCNE, values of xi for the non-alternant hydrocarbons in table 3 have been interpolated and are included in that table. These agree well with those obtained from similar data2 especially for the benzofluorenes, thereby supporting the choice of parameters in table 2.~ V C T TCNE complexes (ev) FIG. 2.-Plot of ~ V C T for complexes of TCNE with various donors against the highest-occupied molecular orbital parameters xi for the donors. A, including benzenoid donors slope = 0.26 ; intercept = 0.01 ; B, excluding benzenoid donors slope = 0.24 ; intercept = 0.04. Butadiene was not included in the computation of the slopes. The numbering is as in table 3. The value for p obtained from fig. 2 (- 3.8 eV) is more negative than that obtained from similar plots by Dewar and co-workers la, 5 (ca. -3.0 eV), and the intercept less so. Values of this intercept (Aj-a) for a given acceptor vary with the series of donors from which they are obtained. Thus while this intercept should not be used to give absolute values of A,, relative values for different acceptors obtained using the same series of donors should be physically significant.Lepley2 has shown that, for alternant hydrocarbons, a plot of the energies of the first charge-transfer bands of these donors with a given acceptor against the energies of the internal electronic transitions of the donor molecules, arising from the promotion of an electron from the highest-occupied molecular orbital into the lowest-occupied molecular orbital, should be linear, and have a slope of one-half. He found that for complexes with 2,4,7-trinitrofluorenone as acceptor this was very nearly so and that a number of non-alternant hydrocarbons more or less obeyed this relationship. From a consideration of eqn. (1) and (2) and the energy of the donor transition given by hv =‘Dj-D], ( 5 )26 C €I A R G E - T R A N S FER C 0 M P LE X E S a more general expression relating the charge-transfer and electronic transition energies is given by Y where (Aj- a) will be a constant for a given acceptor A and hv = internal electronic transition energy for the donor molecule. Thus, for non-alternant donors there will only be an approximately linear relationship between h v c ~ and hv, and the slope should be somewhat less than one-half (see table 3).In fig. 3 the charge-transfer band energies are plotted against the transition energies of the p-bands of the arom- atic donors of table 3, the slope of this approximate linear relationship being 0.49 ; this value is higher than might have been expected owing to the inclusion of the alternant hydrocarbons.40 4 5 5 3 5 5 6 0 -7 5 h v c ~ TCNE complexes (ev) FIG. 3.--Plot of the energy of the p-band transition (hv) for the aromatic donors against the energy of the charge-transfer transition ( h v c ~ ) of their TCNE complexes in chloroform. The numbering is as in table 3. Slope = 0.49 ; intercept = 0.05. Although Lepleyz noted that the plot of ~ V C T against hv for the non-alternant hydrocarbons used in his study of 2,4,7-trinitrofluorenone complexes appeared to parallel the line for the alternant hydrocarbons (slope = 0.54), a separate least- sauares analysis of his data for the non-alternants indicates an approximate linear relationship having a slope of 0.27. Most of the donors used in his work are sym- metrical with respect to a plane bisecting the 5-membered ring, and the highest- occupied and lowest-occupied orbitals in these molecules may tend to become equally spaced above and below the arbitrary zero (the coulomb integral for carbon) with increasing annellation, the value of x-i/(xi + xj) thus approaching one-half, From eqn.(6) the intercept of fig. 3 should be identical with that of fig. 2 and this is found to be approximately the case. IONIZATION POTENTIALS The expression deduced by Matsen 28 relating the energy of the charge-transfer transition for the Complexes formed by a series of donors with the same acceptor to the donor ionization potential ID is izv,, = al,+ b, (7)A . R . COOPER, C . W. P . CROWNE AND P . G . FARRELL 27 where a and b are constants. A number of equations of this form have been pro- posed to evaluate ionization potentials 69 7 and in the present work the values of a and b proposed by one of us for substituted benzene-TCNE complexes are used, kvCT = 0.82I,-4.28 eV.(XI7 Ionization potentials calculated from eqn. (8) are shown in table 3 with those calculated or measured by other workers where available. The values obtained for the ionization potentials of the model alternant hydrocarbons agree well with their measured values thus in part justifying the use of eqn. (8). (As alternant aromatic hydrocarbons are essentially substituted benzenes it is reasonable to suppose that this expression should be generally applicable to TCNE complexes with alternant aromatic donor molecules.) The ionization potential obtained from (8) for thiophen is in reasonable agree- ment with its measured value 27 as would be expected from this donor’s similarity to benzene.Calculated values for the other sulphur-containing donors are probably equally close to their true values for similar reasons. Our calculated ionization potentials for the non-alternant hydrocarbons are 0.6-0.7 eV lower than those calculated by Streitwieser 29 in a molecular orbital study using the o-technique (table 3). This difference is in the same direction and of similar magnitude as that between our value and his for dipheny1,ag and also between his value for azulene (8.32 eV) and that found from charge-transfer data (7.4-7-5 eV).3o However, Streitwieser’s values were obtained using a correlation curve based on experimental electron-impact values, and these are greater than the photo-ionization values from which (8) was derived.73 31 In general, ionization potential values deduced from charge-transfer spectra agree well with those measured by a photo-ionization technique, suggesting that these latter values are closer to the vertical transitions involved in charge-transfer complexes.Apart from the experimentally measured values for furan 329 33 (see table 3), no ionization potential data except from the work of Streitwieser 29 are available for the oxygen heterocyclics. Although we have used only three oxygenated donors, the differences between our values and Streitwieser’s are similar in magnitude for the symmetrical donors (ca. 0.34 eV), and this difference is greater than that for benzofuran (0.20 eV).Also, the difference between the photo-ionization values and Streitwieser’s values for oxygen compounds containing an ethereal oxygen atom is of similar magnitude and in the same direction9 Although furan readily forms a Diels-Alder adduct with maleic anhydride,34 there was no evidence of re- action with TCNE during experiments which might have given rise to a low energy absorption band, thus accounting for the low ionization potential from eqn. (8). This may be an isolated anomaly but throws doubt upon the validity of our cal- culated values for the other oxygen heterocyclics, and owing to a lack of any other experimental data for these molecules, no conclusions other than the fact that the apparent ionization potential decreases as expected with annellation can be drawn.The nitrogen heterocyclics show by far the greatest reactivity of the donors studied towards TCNE and the calculated ionization potentials are lower than those for the sulphur and oxygen analogues, whereas from a consideration of the electro- negativity of the heteroatoms it might be expected that the nitrogen-containing donors would have values intermediate between those for the other two series. The value for pyrrole agrees well with that of Watanabe 33 using a photo-ionization method, although this figure is unique in being substantially lower than any other experimental value (see table 3). The molecular orbital calculations predict that the highest-occupied orbitals for28 CHARGE-TRANSFER COMPLEXES furan, pyrrole and butadiene should have the same energy.The similarity between furan and butadiene has been mentioned above, even though the latter exists in the trans form, and the calculated ionization potential for butadiene is also approxi- mately 0.3 eV lower than the experimental photo-ionization value. Again, there was no measurable adduct formation between TCNE and the donor during the period of the investigation. We are grateful to Dr. R. Grinter for computer facilities and helpful discussions, to Dr. R. E. Benson (E. I. Dupont de Nemours and Company) for a sample of pure 7,7,8,8-tetracyanoquinodimethane, and to Sir John Cass College for financial support (to A. R. C.). 1 (a) Dewar and Rogers, J. Amer. Chem. SOC., 1962, 84, 395. (b) Vars, Pickett and Tripp, J. Physic. Chem., 1962, 66, 1754.(c) Champion, Foster and Mackie, J. Chem. SOC., 1961, 5060. Farnum, Atkinson and Lothrop, J. Org. Chem., 1961, 26, 3204. Das et al., Chem. and Ind., 1963, 866. ZLepley, J. Amer. Chem. SOC., 1962, 84, 3577. 3 Lang, J. Amer. Chem. Sac., 1962, 84,4438. 4(u) Foster and Hanson, Tetrahedron, 1965, 21, 255. (6) Foster and Hanson, Trans. Fwaduy SOC., 1964, 60, 2189. 5 Bhattacharya and Basu, Truns. Farauhy SOC., 1958, 54, 1286. Dewar and Lepley, J. Amer. Chem. SOC., 1961,83,4560. 6 (a) McConnell, Ham and Platt, J. Chem. Physics, 1953. 21, 66. Foster, Tetrahedron, 1960, 10, 96. Kinoshita, Bull. Chem. Sac. Japait, 1962, 35, 1609. Voigt and Reid, J. Amer. Chem. SOC., 1964, 86, 3930. Kuroda, Kubayashi, Kinoshita and Takemoto, J. Chem. Physics, 1962, 36, 457. (b) Briegleb, Angew. Chem. Int. Ed., 1964, 3, 617. 7 Farrell and Newton, J. Physic. Chem., 1965, 69, 3506. 8 Organic Syntheses, 24, p. 33. 9 Shepard, Winslow and Johnson, J. Amer. Chem. SOC., 1930,52,2087. 10 Cairns et al., J. Amer. Chem. SOC., 1958, 80, 2775. 11 Foster and Thomson, Trans. Faraday Soc., 1963, 59,2287. 12 Vogel, A Textbook of Practical Organic Chemistry (Longmans Green and Co., 1951), p. 176. 13 Vogel, A Textbook of Fructical Organic Chemistry (Longmans Green and Co., 1951), p. 167. 14 Benesi and Hildebrand, J. Amer. Chem. SOC., 1949,76,2703. 15 Sausen, Engelhardt and Middleton, J. Amer. Chem. Soc., 1958, 80,2815. 16 Keefer and Andrews, J. Amer. Chem. SOC., 1955,77, 2164. 17 Foster, Nature, 1958, 181, 337. 18 Murrell, The Theory of the Electronic Spectra of Organic Molecules (Methuen, 1963). 19 Middleton, Heckert, Little and Krespan, J. Amer. Chem. SOC., 1958, 80, 2783. 20 McKusick, Heckert, Cairns, Coffman, and Mower, J. Amer. Chem. SOC., 1958, 80, 2806. 21 Briegleb, Elektronen-Donator-Acceptor-Komglex (Springer-Verlag, 1961). 22 Farrell and Newton, unpublished results. 23 Andrews and Keefer, Molecular Complexes in Organic Chemistry (Holden-Day Inc., 1964). 24 Hiickel, Z. Physik., 1931,70,204. 25 Pullman and Pullman, Quaatum Biochemistry (Interscience, 1963). Streitwieser, Molecular Orbital Theory for Organic Chemists (Wiley, 1961). 26 Longuet-Higgins, Trans. Faraday Soc., 1949, 45, 173. 27 Omura, Baba and Higashi, J. Physic. Sac. Japan, 1955, 80, 317. 28 Matsen, J. Chem. Physics, 1956,24, 602. 29 Streitwieser, J. Amer. Chem. SOC., 1960, 82, 4123. 30 Finch, J. Chem. SOC., 1954,2272. 31 Watanabe, J. Chem. Physics, 1957, 26, 542. 32 Watanabe, J. Chem. Physics, 1958, 29, 48. 33 Watanabe and Nakayama, ASTIA Report no. AD-152934. 34 Van-Campen and Johnson, J. Amer. Chem. Soc., 1933,554 430. Morrison and Nicholson, J. Chem. Physics, 1952, 28, 1021.

ISSN:0014-7672    

DOI:10.1039/TF9666200018

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No.13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Spectroscopic Studies on n-Donor + cr-Acceptor Systems: Alkylthioureas and Thiocarbanilides BY K. R. BHASKAR,* R. K. GOSAW 7 AND C. N. R. RAO t Received 6th May, 1965 The donor-acceptor interactions of alkylthioureas and thiocarbanilides with halogens have been investigated in detail employing electronic and infra-red spectroscopy. Various correlations of the spectroscopic and thermodynamic data have been presented. Alkylthioureas are by far the strongest donors known, and give high equilibrium constants (10,000-40,000 1. mole-1) and en- thalpies of formation (9-1 8 kcal mole-1).The perturbation of the various vibrational frequencies due to charge transfer have also been studied. Hydrogen bonding of thioureas with hydroxylic compounds have been reported. Of the various donor-acceptor systems, the n-donor-o-acceptor complexes are associated with high thermodynamic stability.lp2 Complexes of various n-donors with halogens have stabilities that differ considerably from one donor to another, the heats of formation of iodine adducts varying from - 3 to - 12 kcal/rnole. The amine +halogen complexes are the strongest complexes known.192 It was con- sidered of interest to study the complexes of sulphur donors with halogen in view of the limited information available on these systems in the literature.Sulphur would be expected to be a good donor atom since its ionization potential is relatively small. Further, the n+n* transitions of thiocarbonyl compounds 3-5 occur at much longer wavelengths than the corresponding carbonyl compounds. As part of a programme in the study of donor-acceptor complexes of thiocarbonyl com- pounds with halogens and hydroxylic compounds, we have investigated the spectro- scopy and thermodynamics of charge-transfer complexes of alkyl substituted thio- ureas and substituted thiocarbanilides with halogens and phenols. Alkyl sub- stituted thioureas were expected to be powerful donors because of the high electron donating ability of the alkylamino groups. When these studies were in progress, a paper by Drago and co-workers 6 appeared, which included the charge-transfer interaction of tetramethylthiourea with iodine ; this system forms only a small part of the studies reported here.It is possible that in thiourea derivatives the donor site could either be nitrogen or sulphur, as has been observed in transition metal complexes of some substituted thioureas.7~ 8 This study would therefore provide information on the donor site in substituted thioureas compared to thiourea itself, where the donor atom is sulphur.9~ 10 It would also be of interest to examine the effect of substituents in donor. molecules on the magnitude of donor-acceptor interaction and correlate the data, if possible, with substituent constants of the aliphatic and aromatic series. Some studies have also been carried out on solvent effects on the spectra and equilibria of complexes of thioureas with halogens.Detailed studies on the infra-red spectra of thioamides, thioureas and related systems 7 3 11 have shown that in all these systems the C=S stretching vibration is not localized and there is considerable mixing of vibrations. The effect of charge- transfer to iodine on the infra-red spectra of thioureas have been studied with * Dept. of Lnorganic and Physical Chemistry, Indian Institute of Science, Bangalore-12, India 29 Department of Chemistry, Indian Institute of Technology, Kanpur, India30 rt-DONOR +O-ACCEPTOR SYSTEMS particular reference to the mixed vibrations. Such a study would throw some light on the structure of the donor-acceptor complexes. Equilibrium constants and en- thalpies of the hydrogen-bonded complexes of thioureas with phenol have also been reported.EXPERIMENTAL Other than thiourea, all other alkyl and dialkylthioureas were prepared in this laboratory by the addition of amines to the corresponding isothiocyanates and purified before use. Tetramethylthiourea was kindly provided by Dr. M. J. Janssen of Netherlands. All the substituted thiocarbanilides were prepared by the reaction of anilines with carbon disulphide and purified before use. All the other compounds and solvents used were of analytical grade. The measurements of electronic spectra were made on a Hilger Uvispek, Beckman D.U. or a Cary 14R spectrophotometer. The infra-red spectra were recorded with a Carl Zeiss-URIO spectrometer fitted with LiF, NaCl and KBr prisms.The equilibrium constants of formation K of 1 : 1 complexes of thioureas with halogens were calculated using a modified Benesi-Hildebrand equation,9 where [I] is the initial molar concentration of iodine, [D] is the initial molar concentration of the donor, A is the absorbance due to the complex measured in a cell of 1 cm path and E is the molar extinction coefficient of the complex. For alkylthioureas the equilibrium constants were calculated by measuring the absorbance at the Amax of the charge-transfer band, for six solutions with an eight- to ten-fold variation in the thiourea concentration and a constant iodine concentration. At the concentrations employed, iodine had no [mJ31IA = (PI+ [Dl--AIEN/k 1.0 2.0 3.0 FIG. 1.-Typical plots employed in the calculation of equilibrium constants of formation of the alkylthiourea + 12 complexes : N,N'-diethylthiourea (full circle) ; N,N'-di-t-butylthiourea (open circle).([I[]+ PI --AM x 104 absorption in this region and the corrections for donor absorption were also small. The above equation was solved for E with the experimental data for any two solutions and a least-square plot of [I]lr>]/A against ([I]+ [D]-A/E) was made employing data from all the solutions. Using the E obtained from the slope of the resulting straight line a fresh plot of [I][D]/A against ([I]+ [D]- A/&) was made again by least-square procedure and this process was repeated until two successive values of E and K were in good agreement. Two typical plots obtained finally by this procedure are shown in fig.1. There was little or no contribution from contact c.t. pairs to the absorption intensity at the wavelengths employed.K . R . BHASKAR, R . K . GOSAVI A N D C . N. R . RAO 31 For thiocarbanilides, no unique charge-transfer band was observed as there was con- siderable overlap of the donor and charge-transfer absorption. The equilibrium constants were therefore evaluated by measuring the absorbance of the thiocarbanilide+ iodine solutions at three wavelengths in the region 400-420 mp where the blue-shifted iodine band was found to occur as a shoulder on the main band around 312 mp. Fairly good corres- pondence was obtained between the values of K calculated at the three wavelengths. The enthalpies AH" of formation of the donor-acceptor Complexes were evaluated from the equilibrium constants at different temperatures in the range 0-35°C.The equilibrium constants and enthalpies of formation of hydrogen-bonded complexes of thioureas with phenols were studied by employing the free 0-H stretching bands at low concentrations of phenol (where phenol was only monomeric). The frequency shift of the free 0-H stretching band is directly proportional to the AH" of hydrogen bonding 12 and the equation - AH" (kcal mole-1) = 0.016 Av0-~+0.63 has been found to be obeyed by over 50 donors13 including carbonyl and phosphoryl compounds, amines, nitriles, etc. RESULTS AND DISCUSSION The spectra of dialkylthiourea + 12 solutions with different concentrations of the donor and the acceptor are shown in fig. 2 and 3.The development of the charge-transfer (c.t.) band is clearly seen in fig. 2a, where the variation of the inten- sity of the donor absorption band (A, 259 mp) as well as the c.t. band (A,,,, 0.6 0.4 3.2 A (mP) FIG. 2.-Absorption spectra of N,N'-di-t-butylthiourea + I2 complex in CH2C12. (a) Curves 2-4 : effect of varying iodine concentration (in the range 1-25 x 10-5 M) keeping donor concentration constant (at 4.9 x 10-5 M) ; curve 1 : absorption spectrum of the pure donor at the same concentration. (b) Effect of varying donor concentration (in the range 1-2 x 10-5 to 1.5 x 10-4 M) keeping the iodine concentration constant (at 5-1 x 10-4 M) ; spectrum of the pure acceptor is shown by the dotted curve. 305 mp) with the concentration of the acceptor are indicated. The donor absorption band at 259 mp is likely to be due to the n+a* transition of the thiocarbonyl group and there is no variation in the position of this band on charge-transfer with iodine.The c.t. bands of the alkylthiourea+I? complexes (A,,,~298-334 mp) are in the32 PI-DONOR +a-ACCEPTOR SYSTEMS same region as the n+n* transition absorption maxima of these donors (-280- 305 mp). In fig. 2b, the variations of the iodine absorption band (Im,,, 509 mp) with donor concentration are shown at sufficiently high concentrations of iodine. Fig. 3 shows how drastically the visible absorption band of iodine is shifted when the donor concentration is sufficiently high. In -the concentration ranges normally employed 1 400 4 5 0 500 (mp) FIG. 3.-Effect of high donor concentration (-8 x 10-4 M) on the visible absorption band of iodine (concentration -1.0 x 10-4 M) ; CCl4 solvent (dotted line) ; CHC13 solvent (full line). TABLE SP SPECTROSCOPIC DATA ON THE CHARGE-TRANSFER BAND OF n-0 COMPLEXES OF ALKYL THIOUREAS, R2R2N(CS)NR3&, WITH IODINE a IN CHLOROFORM R1 R2 R3 R4 2, m p &max :$; f D,Debye H H H H H H H H H H H H H H H H H H CH3 CH3 298.0 300.5 302.0 304-0 305.5 307.5 304.0 306.5 305.5 334-0 52,000 44,000 40,350 38,700 38,870 38,000 39,960 42,000 37,100 36,600 5,400 5,400 5,600 5,700 5,880 5,600 5,600 5,700 5,600 5,300 1.20 8.75 1.03 8.11 0.98 7.92 0.98 7.96 0.93 7.78 0.93 7.80 0.97 7.93 1.03 8-20 0.90 7-64 1-10 8.82 (a) The blue shifted iodine band appeared as a shoulder in the wavelength region, 396-410 mp.(b) data of Lang.9 (c) with ICl gave a c.t.band at A 305 my; with ICN gave a c.t. band at A 307 mp; with Br2 gave a c.t. band at A 282 my. for the determination of 1 : 1 complexes of alkyl thioureas with iodine, the iodine band is shifted to very low wavelengths and appears only as a shoulder on the c.t. band. The intensity of the c.t. band varies markedly with the donor as well as the acceptor concentrations indicating that the c.t. band is due to complex formation. The spectroscopic data on the c.t. band of alkylthiourea+I2 complexes have been summarized in table 1. Examination of the data in the table shows that the oscillator strengths, half-intensity band widths, transition moments and the blue- shifts of the iodine band are all sufficiently high, indicating fairly strong interactionK .R . BHASKAR, R . K . GOSAVI AND C. N . R . RAO 33 between the donor and the acceptor. The c.t. transition energy of the alkylthio- ureas decreases with increasing electron donating ability of the substituent. Thus, N,N'-di-t-butylthiourea gives a c.t. band at a longer wavelength than N,N'-dimethyl- thiourea. Tetramethylthiourea is out of line probably because of the difference in con- formation.3~ 7 A similar behaviour is also noticed in the n +n* transition of the thio- carbonyl group in alkylthioureas,7 where the n +n* transition energy in disubstituted thioureas vary in the order t-butyl < i-propyl <ethyl <methyl. The n +n* transition energy of tetramethylthiourea is much lower than can be accounted for by simple substituent effects.r( 3 E 3 20- 0 oj 8 - %- d IO- I TABLE 2.-THERMODYNAMIC DATA ON THE IODINE COMPLEXES OF THIOUREAS, RlRzN(CS)NR3R4, in CHLOROFORM ,/' 1 1 I I 1 I I -AF" -AH" -ASo kcal kcal cal/mole bZ/az Taft (5* concentration of thiourea a 1. mole-1 mole-l mole-1 deg. RI Rz R3 R4 H H H H H H H H H H H H H H H H H H CH3 CH3 0-6-3.6 X 10-4 M 0.56-5.6 X 10-4 M 036-3.7 X 10-4 M 037-3.7 x 10-4 M 037-3.7 x 10-4 M 043-3.9 x 10-4 M 041-4.1 x 10-4 M 0.54-5.4 X 10-4 M 0.4544 X 10-4 M 0-37-3-7 X 10-4 M 4,400 5.10 9.6 13,100 5.80 - 14,960 5.80 + 15,520 5.80 14.4 16,430 5.90 11.3 40,860 6.50 18.6 17,130 5.90 - 20,820 6.00 - 10,350 5.60 - 13,560 5-80 9.5 a Concentration of iodine used was in the range 0.2-03 x 10-4 M, temp. 25-26°C b data of Lang.9 c with ICN gave a K of 12,700 at 255°C.Thermodynamic data on the iodine complexes of alkylthioureas are shown in table 2. The equilibrium constants and enthalpies of formation are generally large. The AF" (= -RT In K ) values show fairly linear relation (with tetramethylthiourea as an exception) with the Taft 14 aliphatic polar substituent constants, (T*. Similar correlations with o* have been found for charge transfer complexes of aliphatic amides.15 The AH" and the AS" of the alkylthiourea+I2 complexes are also linearly related (fig. 4) as observed earlier by Tamres and Brandon 16 in other systems. The enthalpies are by far the highest values encountered in any donor-acceptor system. The complex of N,N'-di-t-butylthiourea with iodine should be particularly noted for its high K (40,860 1. mole-1) and AH" (- 18.6 kcal mole-1). The K and AH" values of amides and urea derivatives 1 7 9 18 are much smaller than those encountered in this study.Considering the high f (c.t.), K and AH" values of these 234 72-DONOR + G-ACCEPTOR SYSTEMS thiourea + I2 complexes, one would expect from the simple charge-transfer theory 2 that the coefficients a and b of the no-bond and dative wave functions would be quite similar in magnitude to those encountered in the aminefiodine systems. the ratio b2/& was evaluated for the alkyltliiourea+I2 systems and the values are tabulated in table 2. The ratio varies between 0-1-0.2, which is high compared even to the strong amino+iodine systems which give values of the order of 0-1 by the same method of evaluation. This method of evaluation of b2/& from - AHo/hvc.t. gives values lower than those obtained from dipole moment data.20 One may, however, conclude from this study that the magnitude of interaction between the donor and acceptor is very high in the thioureafI2 system.The overlap integral Sol should also be high considering the large blue-shifts of the visible iodine band. The values of Sol and the corresponding matrix element Po for these systems 1 9 2 are expected to be ca. 0.3 and -2.5 eV respectively, since there is likely to be closer approach of the donor and acceptor molecules as in the amiiie+I2 system. Un- fortunately, no ionization potential data are available for the thioureas to evaluate Sol and PO from the relationship between hvc.t. and the vertical ionization potential.1 Making use of the relation 169 19, 20 b2/azx - AH"/hVc.t., TABLE 3.-sPECTROSCOPIC AND EQUILIBRIUM DATA ON THE IODINE COMPLEXES OF THIOCARBANILIDES, (RCbH4NH)lC=S solvent : CHC13 (25"-26"C) E K, 1.mole-1 --Fa - &t., concentration of A average kcat 3, 1 A 1 mole-1 mp thiocarbanilide a __ R (4000 .&) (41 00 A) (4200 A) (4200 A) (4 100 A) (4200 A) p-OCH3 -0.27 314 1*05-10*5 >< 10-4 M 5,000 4,450 3,830 13,490 14,320 14,220 14,010 5.66 p-CH3 b -0.17 313 1.1-11.1 X 10-4 4,800 4,330 3,780 11,030 11,700 12,140 11,620 5.55 1350 & 400 HC 0.0 312 1*09-109X10-4 4,240 3,920 3,490 6,510 6,560 6,640 6,570 5.21 -&50 p-Br +0.23 318 2.65-21.2~ 10-4 3,870 3,520 3,160 2,180 2,310 2,480 2,320 4.59 a concentration of iodine used was in all cases -1.1 x 10-4 M ; * with Br2 gave a K of 7950 ; AH with iodine wi?s - 7.0 kcal/mole ; c with BrZ gave a K of 3715.i 105 Solvent effect studies on the c.t. bands and equilibria of the alkylthiourea+T2 complexes have shown that the hvc.t. generally increases with the dielectric constant of the solvent. Similar increase in transition energies with the polarity (2 values) of the solvent has been observed by Kosower,21 for strong intramolecular c.t. transi- tions. The increase of hvc.t. with dielectric constant of the solvent for these complexes parallels the increase in the n +n* transition energies with dielectric constant.3-5 The equilibrium constants do not show much variation in chloroform and carbon tetrachloride for dialkylthiourea complexes. However, with tetramethylthiourea there is a marked increase in the equilibrium constant in chloroform as compared to carbon tetrachloride, the value in the latter solvent agreeing well with that re- ported by Drago.6 However, the enthalpy values are nearly the same in the two solvents.Some instances where the equilibrium constant varies with solvents have been reported9 The solvent effects noticed in this study can only be rationalized in terms of the generalizations of Mulliken,23 who has pointed out the importance of dipole-dipole, van der Waals and other non-specific interactions between solute and solvent molecules in his charge-transfer theory. Solvent effects have beenK . R . BHASKAR, R . K . GOSAVI A N D C . N. R . RAO 35 employed for the evaluation of a and b of charge transfer complexes by Chakrabarti and Basu,24 for some weak complexes. Although, strictly speaking, the equation developed by Chakrabarti and Basu24 cannot be used for strong complexes with very high oscillator strengths, it was employed to give an approximate value for the ratio of the ground and excited state dipole moments.With N,N'-di-i-propyl- thiourea, the ratio was found to be -0.1 compared to -0.01 for the weak complexes studied by Chakrabarti and Basu.24 Although this is in the right direction, inferences from solvent induced frequency shifts are generally uncertain due to relaxation times needed for maximum stabilization of the polar excited state by solvent molecules. In addition to alkylthioureas, the c.t. complexes of a few thiocarbanilides with iodine have been investigated and the data are summarized in table 3.Typical absorption curves of thiocarbanilide+I2 are shown in fig. 5. The equilibrium 280 300 320 340 (4 (mcL> (b) FIG. 5.-Absorption spectra of thiocarbanilide+ 12 in CHC13 : (a) Lower curve : the absorption spectrum of pure donor (at 3 . 6 ~ 10-5 M); upper curve, donor+& (I2 at 3.5 x 16)-5 M) ; the c.t. band is shown by dotted line. (b) Lower curve : visible absorption band of iodine (concentration 1.33 x 10-4 M) ; upper curve : visible absorption of iodine (conc. 1-33 x 10-4 M)+donor (concentration 9-2 x 10-4 M). constants are fairly high and increase with increasing electron donating ability of the substituents on the benzene ring. Thus, the equilibrium constant is highest for p,p'-dimethoxy thiocarbanilide and lowest for p,p'-dibromothiocarbanilide.Linear relations are found between the AF" and the Hammett CT constants as well as between the band extinctions and the CT constants.25 Such correlations with 0 constants have been reported for the equilibrium constants of formation of charge transfer complexes of thioanisoles with iodine3 The correspondence between the c.t. and the n+n* transition energies as well as the direction of substituent effects on the c.t. equilibria indicate that sulphur is probably the donor atom in these systems. Lang 9 has argued in favour of sulphur as donor atom in thiourea and Drago 6 has presented some indirect evidence from n.m.r. spectra. If sulphur is the donor atom, it is most likely that the iodine mole- cule lies axially with the thiocarbonyl group as with the other n-donor+iodine systems.11 2, 20 This conclusion finds support from the infra-red studies reported here.The effect of charge-transfer with iodine on the major infra-red bands (with tentative assignments 7) of dialkylthioureas are shown in table 4. The variation36 rt-DONOR + o-ACCEPTOR SYSTEMS of the band intensity on charge-transfer is also indicated in the table. The fre- quency of the mixed vibrations involving either C-N or C=S stretching vibra- tions are all affected greatly on charge-transfer. The mixed vibration frequency in the region 975-1050 cm-1, which is probably associated with a high percentage of the C=S stretching Vibration, decreases on charge transfer and the band is in- tensified as one would expect if sulphur were the donor atom.The N-C-S bending vibration frequency increases while the intensity decreases on charge TABLE 4.-EFFECT OF CHARGE TRANSFER WITH IODINE ON THE MAJOR INFRA-RED BANDS OF DIALKYLTHIOUREAS, RlNHC(S)NHRz R1=CH3, effect of R z = ~ - G H ~ charge RI, Rz=CH3 R1, Rz=CzH5 R1, Rz=i-C3H7 R1, Rz=t-C4Hg tentative unperturbed unperturbed mperturbed unperturbed unperturbed transfer +I? on band cm-1 cm-1 intensity assignmentsa bands +I2 bands +I2 bands +I2 bands +tIz bands cm-1 cm-1 cm-1 cm-1 crn-1 cm-1 cm-1 cm-1 vNH(free) ~ N H +YC-N SNH+ YC-N YNCN + yc-s ~ N H + YCN mainly YC-" (NH-C= SI) (NH-C=SI) (NH-c=~ 11) *C-" + VC=S N-H-C=S IV (NH-C=S (111) SNCN 'NCS 3440 3423 3428 3413 3415 1549 3402 3445 3412 1550 3430 3334 1552 3462 3415 1551 3448 340 1 1568 decrease 1555 1586 1553 1577 1565 increase 1504 1354 1514 1370 1499 1340 1504 1340 1286 1088 1043 892 538 1495 1348 1276 1086 1055 1504 1349 1270 1078 1040 1505 1506 1326 1289 1118 1010 1503 1340 1278 1063 1033 1504 1335 1292 1162 1028 decrease slight decrease increase increase increase little change slight increase decrease 1325 1280 1118 1048 1290 1088 1048 882 1288 1088 1030 88 1 534 1285 1091 1063 889 563 878 578 878 560 932 548 905 506 472 887 579 879 555 55 1 4 8 463 458 483 47 1 488 459 463 445 498 464 a assignments of Rao and Venkararaghavan 11 and Gosavi and Rao 7 TABLE 5.-EFFECT OF CHARGE-TRANSFER WITH IODINE ON THE MAJOR INFRA-RED BANDS OF TETRAMETHYLTHIOUREA," (CH3)2NC(S)N(CH3)2 unperturbed bands +iodine cm-1 cm-1 effect on band intensity tentative assignments 1505 1556 1469 1469 1380 1380 1361 1392 1140 1154 1115 1109 1097 1096 1064 1060 885 879 493 476 increases no change slightly increases increases decreases large increase increases decreases slightly decreases - (a) assignments of Gosavi and Ra0.7 transfer.The N-H bonds in most dialkylthioureas have a trans-configuration with respect to the C=S bond and both the free N-H stretching frequency and intensity decrease on addition of iodine. With N,N'-di-t-butylthiourea, where both cis and trans configurations seem to exist,7 the cis-N-H band shows greater decrease in frequency and intensity. The variation of the N-H stretching bands on addition of iodine is mainly due to hydrogen bonding with iodine since excess of iodine is present under the experimental conditions.The bonded N-H stretching vibrations also show coiisiderable variation on addition of iodine as expected.K . R. BHASKAR, R. K . GQSAVI AND C . N. R. RAO 37 In table 5, the effect of charge-transfer on the major infra-red absorption bands of tetramethylthiourea are shown. All the bands which have some contribution from C-N and C=S stretching frequencies show maximum variation in frequency and intensity. In particular, the frequency of the band at 1150 cm-1 which is mainly due to C=S stretching decreases on charge-transfer while the intensity increases. Hydrogen bonding studies on alkylthioureas with phenols have been carried out. The AVOH and the thermodynamic quantities are summarized in table 6. The AF" and AH" bear a rough linear relation with each other.The n+n* blue- shifts 5 of the C=S chromophore in ethanol are also summarized in table 6 for TABLE 6.-TEaERMODYNAMIC DATA ON THE HYDROGEN BONDING OF THIOUREAS R I R ~ N C ( S ) R ~ R ~ WITH HYDROXY COMPOUNDS infra-red studied of hydrogen bonding with phenol R4 Av,,*, cm-1 AvO-H - AF' (23°C) - AHo - AS0 R1 R2 R3 cm-1 kcal mole-1 kcal mole-1 cal/mole deg. C2H5 H C2H.5 H 21 3 1.40 4.04 8.92 2060 CH3 H t-C4M9 H 223 1-36 4.20 9.59 1880 t-C4H9 H t-C4H9 H 218 1.59 4.12 8-54 1140 CH3 H C&'5CH2 H 208 1 *03 3.96 9.73 2140 CHI CH3 CH3 CH3 263 1.03 4.84 12.87 1910 CH3 H i-C3H7 H 213 1-34 4-04 9.12 1700 (a) in trichloroethylene solvent with phenol concentration at 0,007 M. (b) blue-shift in ethanol compared to ether as solvent. purposes of comparison.There seems little doubt that the donor site for hydrogen bonding is sulphur, particularly in view of the blue shift of the n+n* transition of the thiocarbonyl group in proton-donor solvents. The AH" of hydrogen bond- ing (table 6) does not vary appreciably with substituents, while the AH" for the interaction with iodine varies drastically ( - 9 to - I8 kcal mole-1). Thus, the nature and magnitude of interaction between the donors and acceptors in the two systems are not exactly the same. The authors' thanks are due to the Indian Institute of Science, Bangalore, and the Indian Institute of Technology, Kanpur, for awards of research scholarships. Their thanks are also due to Prof. M. R. A. Rao for his interest. Note added in proof: The first ionization potential of tetramethylthiourea lias been found to be 8.12eV by electron impact method. The hvc.t. of this compound falls close to the kvc.t. -ID line of Briegleb 1 rather than the line for amines.1 Thanks are due to Dr. A. €3. King and Dr. J. G. Larson of Gulf Research and Develop- ment Co., Piltsburgh, Fa. 15230, U.S.A., for the measuremeut of ID. 1 Mulliken and Person, Ann. Rev. Physic. Chem., 1962, 13, 107. 2 Mulliken, J. Chim. Physique, 1963, 20. 3 Janssen, Rec. trav. chim., 1960, 79, 454. 4 Rao, Balasubramanian and Rainachandran, J. Sci. Ind. Res. (India), I961 , 20B, 382. 5 Rao, Ultra-violet and Visible Spectroscopy-Chemical Applications (Butterworths, London, 6 Niedzielski, Drago and Middaugh, J. Amer. Chem. SOC., 1964, 86, 1694. 7 Gosavi and Rao, unpublished results. 8 Lane, Yamaguchi, Quagliano, Ryan and Mizushima, J. Amer. Chem. Suc., 1959, 81, 3824. 1961).38 n-DONOR + 0-ACCEPTOR SYSTEMS 9 Lang, J. Anzer. Chem. SOC., 1962, 84, 1185. 10 Yamaguchi, Penland, Mizushima, Lane, Curran and Quagliano, J. Amer. Chern. Soc., 1958, 11 Rao and Venkataraghavan, Spectrochinz. Acta, 1962, 18, 541 ; Can. J. Chem., 1964, 42, 36. 12 Joesten and Drago, J. Amer. Chem. Soc., 1962, 84, 3817. 13 Singh, Murthy and Rao, Trans. Faraday SOC., in press. 14 Taft, Steric Eflects in Organic Chemistry, ed. Newman (John Wiley, New York, 1956). 15Drago, Wenz and Carlson, J. Amer. Chem. SOC., 1962, 84, 1106. 16 Tames and Brandon, J. Amer. Chem. SOC., 1960, 82, 2134. 17 Carlson and Drago, J. Amer. Chem. SOC., 1963, 85, 505. 18 Middaugh, Drago and Niedzielski, J. Amer. Chem. SOC., 1964, 86, 358. 19 Ketelaar, J. Physics Radium, 1954, 15, 197. 20 Briegleb, EZectronen- Donator-Acceptor-KompZexe (Springer-Verlag, Berlin, 1961). 21 Kosower, J. Amer. Chem. Soc., 1958, 80, 3253. 22 Thompson and DeMaine, J. Amer. Chem. SOC., 1963, 85, 3096. 23 Mulliken, J. Physic. Chem., 1952, 56, 801. 24 Chakrabarty and Basu, Trans. Faraduy SOC., 1963, 60, 465. 25 McDaniel and Brown, J. Org. Chem., 1958, 23, 420. 26 Van der Veen and Stevens, Rec. trav. chim., 1963, 52, 287. 80, 527.

ISSN:0014-7672    

DOI:10.1039/TF9666200029

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Ring Inversion of Some 1,3-Dioxanes BY J. EDGAR ANDERSON" AND J. C. D. BRAND? The University, Glasgow, W.2. Received 17th March, 1965 Thermodynamic parameters have been determined for the chair-to-boat isomerization of 1,3- dioxane, its 2,2- and 5,5-dimethyl, and 2,2,5,5-tetramethyl-derivatives, in acetone or dichlorodi- fluoromethane solution in the temperature range 120-235°K.The significance of the results is discussed. The inversion of some fifty cyclic compounds has been studied through their nuclear magnetic resonance spectra. However, most have received only passing attention, usually in the form of a simple AG* determination from a coalescence temperature, and the numbcr of substances investigated over a broad band of tem- peratures is small, about ten or twelve. Of them, cyclohexane 1 and its derivatives 2-4 and some 1,2-dioxanes and dithianes 596 have received the greater attention, but no series of compounds has yet been studied to show how the thermodynamic parameters of isomerization change with successive substitutions in the ring. It seemed worth while to examine the conformational isomerization of 1,3-dioxane and some of its methyl derivatives from this point of view, especially since the investigation of assorted ring types, often with only one example of each type, has generally been favoured in the past.Q b C c! FIG. 1 .-(u), 1,3-Dioxane ; (b), 2,2-dimethyl-l,3-dioxane ; (c), 5,5-dimethyl-l,3-dioxane ; (d), 2,2,5,5-tetramethyl-1,3-dioxane. Ring positions in 1,3-dioxane are numbered as shown in fig. 1. Besides the parent structure, the study included the 2,2- and 5,5-dimethyl- and 2,2,5,5-tetra- methyl-derivatives, so that each rate process observed corresponded to the inter- conversion of chair-forms of equal energy and probability. Likewise, each com- pound has at least one signal that at room temperature is a single sharp line, dividing into two chemically-shifted signals or an AB-quartet on cooling ; thus the calculation of relaxation times and rate constants is straightforward.7 Two of the compounds had three resonances that were suitable for treatment simultaneously.A report of similar measurements based only on coalescence temperatures appeared while this work was in progress.8 * present address : Institut de Chimie, UniversitC de Strasbourg. present address : Vanderbilt University, Nashville, Tenn., U.S.A. 3940 RING INVERSION OF SOME 1,3-DIOXANES EXPERIMENTAL 1,3-Dioxane and its methyl derivatives were prepared by condensation of formaldehyde (as paraformaldehyde) or acetone with commercially-available propane-l,3-diol or 2,2- dimethyl propane-l,3-dio1.9 Equilibrium favours the dioxane when formaldehyde is used ; with acetone, water was removed continuously by an azeotropic method.10 The products were purified by chromatography on grade I1 alumina.Dichlorodifluoromethane (Arcton 12), kindly supplied by I.C.I. Ltd., A.R. acetone, and A.R. carbon disulphide were used without purification. Spectra were recorded with an A.E.I. RS2 spectrometer, operating at 60 Mclsec, fitted with a variable-temperature probe. The sample temperature was controlled by a stream of precooled nitrogen in the usual way, and was monitored by a copper-constantan thermo- couple located inside the probe. Since the temperature gradient from sample to thermo- couple depended on the nitrogen flow rate, the thermocouple was calibrated against a model F22 thermistor (Standard Telephones and Cables Ltd.) inserted in a sample tube con- taining low-freezing ethyl acetate.The constants of the thermistor had previously been determined independently over the temperature range 0 to -130°C. To about -6O"C, the calibration checked satisfactorily against the " methanol thermometer ".I1 In this way temperature control was achieved to about f2"C. RATE CONSTANTS Spectra recorded at temperatures corresponding to " slow " or " fast " isomerization were analyzed by standard methods,7 using the equations of Piette and Anderson for the treatment of collapsed spin multiplets.12 The actual T2 was assumed to be controlled by the field inhomogeneity and was determined from the half-width, Av+ = (nT2)-1, of a reference signal (usually acetone) in the same solution, unless Av+ was less than about 1 c/sec, when the constant was obtained from the decay envelope of the " wiggle " pattern, Certain signals gave evidence of broadening by long-range coupling and were discounted.Intermediate rates were calculated from the diminishing separation of two chemically- shifted signals (from a gem-dimethyl group), and from the coalescence temperatures.7 Coalescence of an AB-quartet was interpreted by the equation 13 where z is defined as in ref. (7). The last two treatments were applied with the restriction that T . 9 7 , this condition being checked before the analysis was accepted. The sweep rate used in quantitative experiments was 0.5 c/sec2. Solution concentrations were 0.6 M in all experiments. Acetone, mixed with 10 % carbon disulphide below -lOO"C, was suitable to - 110" but dichlorodifluoromethane was used in those series which extended to lower temperatures.Since the axial and equatorial populations are necessarily equal, (Taxial)-l = (T,qua*o,.ial)-l = (2z)-1. 7-1 is therefore a rate constant which measured the rate of isomerization both ways so that the rate constant desired, i.e., the rate constant for isomerization in one direc- tion, is k = (2z)-1. At each temperature, k was an average of 5-10 individual determina- tions (including, where practicable, determinations from the signals belonging to different ring-methylene or gem-dimethyl groups) which among themselves showed scatter of up to 20 %. This is far from ideal, but the experimental difficulties are severe, especially below - 100°C.RESULTS 1,3-DIOXANE At room temperature the spectrum shows spin multiplets at 8.327 and 6.197 corresponding to the 5-C and 4-C ring hydrogens, and a single peak at 5.197 (2-C protons). At low temperatures the 2-C signal resolves into an AB-quartet in which the pair of lines at low field, corresponding to the equatorial proton,16 is slightlyJ . EDGAR ANDERSON AND J . C . D. BRAND 41 broadened. It is assumed that this is due to coupling with the equatorial proton on 4-C, for its geometrical relation to this proton is suitable whereas that of the axial proton is not.15 The 2-C proton signal was used to evaluate rate constants but one method, viz., that for slow exchange, was not used owing to the unresolved coupling.5,5-DIMETHYL- 1,3-DIOXANE In conditions of fast isomerization the spectrum comprises three single peaks corresponding to the 2-C and 4-C ring protons (5-9i and 6.46~), and the 5-C methyl groups (8.982). On cooling, the first two divide into AB-quartets while the methyl groups appear as chemically-shifted peaks. All three signals yielded rate constants in the appropriate range of temperature. The low-field component of the 2-C quartet and the high-field component of the 4-C quartet are both broader than the other components, probably swing to coupling with one another as before. 2,2-DIMETHYL-1,3-DIOXANE Only the 2-C methyl signal is suitable for rate analysis, for the 4-C and 5-C ring protons give rise to complex multiplets at low temperatures.This dioxane isomerizes rapidly so that the 2-C methyl signal does not divide until the temper- ature is lowered to - 126°C. At - 150°, the peaks are still quite broad but have reached their limiting separation of 10.8 c/sec. It can be shown 16 that part of the broadening at low temperatures is due to long-range coupling between the two non-equivalent methyl groups, so that measurements below the coalescence tem- perature were discounted. 2,233 - TETRA ME THY L -1,3 - D I 0 X A NE At room temperature there are three single peaks, corresponding to the 4-C ring protons (6-46~), and the 2-C and 5-C methyl groups (8.61 and 9.017). On cooling, the 4-C resonance splits into an AB-quartet and the gem-dimethyl peaks into pairs of chemically-shifted signals. Rate data can be obtained from all three signals but as the relative shift of the 2-C methyl groups is small (3.5 clsec), the range of temperatures in which they yield useful results is likewise restricted.S-TRIOXANE A number of measurements were carried out in an attempt to observe division of the signal into an AB-quartet. At -loo", the line width is about 1 c/sec greater than the natural line width. The excess width increased on further reduction of temperature but no splitting was observed down to the limit imposed by solubility considerations. Analysis on the basis that the excess line width in this range should be attributed to motional broadening of a coalesced spectrum gave unreasonable values for AH* (AH* E 1.3 kcal/mole) and the result was rejected. It may be that the resolved spectrum has J A B / ~ A B > 1, when the outer lines of the quartet would be difficult to observe and the inner lines difficult to resolve.The averaged chemical shifts at room temperature and the axial-equatorial splittings and coupling constants observed at low temperatures, together with the coalescence temperatures, are collected in table 1. Change of temperature has no appreciable effect on the average shift. The axial-equatorial chemical shifts vary in a manner not easily foreseen; e.g., the chemical shift of the 2-C methyl groups42 RING INVERSION OF SOME 1,3-DIOXANES in the tetramethyl-compound is only one-third the value found for the same methyl groups in the 2,2-dimethyl-compound. Where comparison is possible, the coupling constants we observe bear out the analysis of the room-temperature spectra of dioxane and its methyl derivatives.16 The temperature-dependence of k was analyzed by the Eyring equation, k = K(kT/h) exp (AS*/R) exp (- AH*/RT). (1) As defined in the previous section, k is the rate constant for the chair-to-chair iso- merization.The isomerization, however, almost certainly takes place through the metastable boat and/or skew boat conformations, and the rate of chair-to-chair compound s-trioxane TABLE 1 a coalescence b J a-c n-e temp. "C group 5-00 - 2-H 5.19 19.3 6.3 4,6-H 6.19 5-H 8.32 85 2,2-dimethyL 4,6-H 6.19 1,3-dioxane 5-H 8.25 2-Me 8.68 10.8 - 126 5,5-dimethyl- 2-H 5.19 30.4 6.0 - 58 1,3-dioxane 4,6-H 6.46 10.3 10.4 - 62 5-Me 8.98 27.1 - 58 2,2,5,5-tetramethyl- 4,6-H 6.46 27-4 12.9 - 100 1,3-dioxane 2-Me 8.61 3.5 - 108 5-Me 9.01 21.5 - 100 a mean chemical shift 7 units (room temp.) b relative shift of axial and equatorial groups, in cisec at 60 Mc/sec.isomerization will then be one-half the rate chair-to-boat. Therefore, in order that AS* (and AG*) in eqn. (1) refer to passage across one barrier, it is necessary to take 7c = 3. The equations used to analyze the rates are then AG&, = 2.303RT[ -log (k/T)+ 10.018], (2) -AH&) = 2*303R[d(log k)/d(l/T) + 2'303RT1, (3) -AS* = d(AG*)/dT. (4) Values of AG*, AH* and AS* obtained are shown in table 2, where recent results for cyclohexane are included for comparison. DISCUSSION It emerges from table 2 that the barriers opposing isomerization in cyclohexane and 1,3-dioxane are, for practical purposes, equal ; any difference between them is within experimental error.The transition state for cyclohexane is uniquely defined -according to Hendrickson 18 it is a " cyclohexene-like " conformation with four adjacent ring atoms lying in the same plane-whereas dioxane possesses three cyclohexene-like states of different energy, as illustrated in fig. 2A. In consequence there are three distinct paths of isomerization, no one of which necessarily cor- responds exactly with AG*. We cannot estimate the spread of activation energiesJ. EDGAR ANDERSON AND J . C. D . BRAND 43 TABLE ACTIVATION PARAMETERS AH* AS * solvent *Gioooc kcal/mole cal/mole deg. compound kcal/mole 1,3-dioxane Me2CO 9.0 10.2 f 1-0 f 6 f 5 2,2-diniethyl-l,3- 5,5-dimethyl- 2,2,5,5-tetramethyl- dioxane F2CC12 7.8 (6.3) a (-7) 1,3-dioxane Me2CO 10.5 12.4 10.8 +9+4 1,3-dioxane Me2CO b 8-2 9.1 f0-9 + 4 f 5 cyclohexane C cs2 10-2(206") 10.5 A0.5 + 1-4i-1-0 a The temperature range was restricted (see results) and the uncertainty was greater than else- between the possible transition states, but the fact that the barriers hindering methyl torsion in propane 19 and dimethyl ether 20 are nearly equal suggests that it may be small.The contrast in behaviour of 2,2-dimethyl dioxane and the 5,5-dimethyl-isomer is less expected. It seems certain that the low value of AG* for 2,2-dimethyldioxane, results from steric compression between the axial 2-methyl group and the axial where in the table ; b below - 11O"C, FzCC12 ; C ref. (1). 5 c D FIG. 2.-(A), cyclohexene-like forms of 1,3-dioxane ; (B) and (C), stable skew-boat forms of 2,2- dimethyl-l,3-dioxane and 2,2,5,5-tetramethyl-1,3-dioxane ; @), cyclohexene-like form of 2,2,5,5- tetramethyl- 1 ,3-dioxane.hydrogen atoms on C-4 and C-6. This interaction, well-known in the cyclohexane series, is intensified in the dioxane system since the CO bond distance is shorter than a CC distance by about 0.1 A. Without distortion, the separation of groups in the axial 2- and 4-positions is about 2.4& much less than the sum of the contact44 RING INVERSION OF SOME 1,3-DIOXANES distances of a methyl group and a hydrogen atom. Thus, the chair form must be distorted in its ground state and the further displacements necessary to attain the transition state are reduced accordingly. Crowding also affects some boat and skew-boat forms of 2,2-dimethyldioxane, though it is absent from the skew-boat conformation shown in fig.2B which represents the most stable of the various non-chair forms. Since the skew-boat forms of cyclohexane lie about 5 kcal/mole above the ground-state chair form,21 it may be that in 2,2-dimethyI-dioxane the relatively stable skew-boat structure shown in the fig. is not much different in energy from the strained chair form; it might itself be the ground state. The last possibility can be discounted, however, for this skew-boat has a two-fold axis of symmetry passing through the ring atoms 2 and 5 so that its methyl groups are symmetrically equivalent. The low-temperature spectrum shows two chemically- shifted signals, which must belong to the chair form.We were unable to observe an extra peak that might correspond to the C(CH3)z signal of the boat conformation, thus we conclude that the contribution of the latter conformation is less than 10 %. In any case, it seems unlikely that interconversion of skew-boats could have a free energy of activation of 7.8 kcal/mole, the value found for the 2,2-dimethyl-compound. Moreover, 2-bromo-3,3,5,5-tetramethylcyclohexanone, where 1,3-diaxial interactions are much greater, has been shown22 to adopt a chair conformation, distorted to accommodate these interactions. We have thus assumed in the analysis of the spectra that the contribution of boat conformations can be ignored. Compared with the 2,2-dimethyl-compound, 5,5-dimethyldioxane has a high value of AG*, higher than dioxane itself.1,3-Diaxial interactions in this case in- volve a methyl group and the lone-pair electrons of oxygen atoms, instead of the methyl-hydrogen interactions which dominate the behaviour of 2,2-dimethyldioxane. Since the free energy of activation is greater than for dioxane it would appear that methyl-lone pair interactions do not distort the ground state appreciably by steric crowding. This is not unexpected in view of recent evidence23 that a nitrogen lone pair fills out a volume similar to covalently bound hydrogen for, according to Slater’s rules, an oxygen orbital is more compact than a nitrogen orbital. The fact that AG* is higher than for dioxane can probably be rationalized on the basis that the opposition of C-H and C-C bonds encompasses a greater energy differ- ential than the opposition of two C--W bonds. Thus, in the branched-chain series ethane, propane, isobutane the barrier opposing methyl torsion rises (2-87,24 3.2,19 4.9 14 kcal/mole, respectively) as C--H bonds are replaced by C-C bonds.The results for tetramethyldioxane probably reflect a complex situation. In the most stable skew-boat form (fig. 2C) the gem-dimethyl groups are equivalent so that the low temperature spectrum, which shows non-equivalent 5-C methyl groups, certainly belongs to the chair conformation. As the ground state must be distorted by 1,3-interactions similar to those present in the 2,2-dimethyl compound, the cyclo- liexene-like structure for isomerization is probably that in which the ring atoms 1,2,3 and 4 (or 6,1,2 and 3) are coplanar (see fig.2D). But this configuration intro- duces appreciable crowding between the 2- and 5-methyl groups on the same side of the ring-their separation is about 3-3&--so that the free energy of activation is greater than for the 2,2-dimethyl compound. In addition, there is 1,2-0pposition of C-C and C-H bonds as in the 5,5-dimethyl compound. In fact, none of the transition-state configurations of tetramethyldioxane is sterically uncrowded, thus, whichever reaction co-ordinate is preferred there must be an appreciable steric contribution to AG*. As to entropies of activation, the extremes of behaviour are represented by dioxane and 2,2-dimethyldioxane. We have already indicated that dioxane probablyJ.EDGAR ANDERSON AND J . C . D. BRAND 45 isomerizes by way of any one of three nearly equivalent " cyclohexerie-like '' con- figurations, and this is consistent with a positive entropy of activation. With 2,2- dimethyldioxane, on the other hand, one co-ordinate is favoured; thus AS* should be less positive, as it is observed to be. This qualitative argument agrees with the observations, but quantitative arguments are less satisfactory and we have been unable to account statistically for more than a part of the difference, about 13 cal/mole deg., between the activation entropies of dioxane and its 2,2-dimethyl- derivative. Allerhand and Gutowsky 25 have pointed out that systematic errors affect AH" and AS* much more markedly than AG*, and that when measurements can be made only over a small range of temperatures, there may be large errors in values of AH* and AS*, though not in A P .In the light of these comments a more de- tailed discussion of the entropies and enthalpies of activation does not seem profitable.? t Note added in proof .- Schmid, Friebolin, Mabuss, and Mecke (Spectrochim. Acta, in press ; private communication) have recently completed a similar investigation of the compounds discussed in this paper.* Results for AG* agree between the two investigations. Agreement is less satisfactory for values of AH* and AS* in the two cases (1,3-dioxane and 2,2-dimethyl-l,3-dioxane) where the temperature range suitable for measurements is smallest, thus bearing out Allerhand and Gutowsky's comments .25 We thank D.S.I.R.and the Stirlingshire Educational Trust for financial support. 1 Bovey, Hood, Anderson and Kornegay, J. Chem. Physics, 1964, 41, 2041 ; and earlier refs. ZTiers, Proc. Chem. SOC., 1960, 389. 3 Bovey, Anderson, Hood and Kornegay, J . Chem. Physics, 1964,40, 3099. 4Brownstein, Can. J. Chem., 1962, 40, 870. 5 Claeson, Androes and Calvin, J . Amer. Chem. SOC., 1961, 83, 4357. 6 Claeson, Androes and Calvin, J. Arner. Chem. SOC., 1960, 82,4428. 7 Pople, Schneider and Bernstein, High Resolution Nuclear Magnetic Resonance (McGraw-Hill, New York, 1959), chap. 10. Friebolin, Kabuss, Maier and Luttringhaus, Tetrahedron Letters, 1962, 683. Boeseken and Hermans, Ber., 1922, 55, 3758. 10 Conrad, Gesner, Levasseur, Murphy and Conrad, J. Org. Chem., 1961,26, 3571. 11 Varian Associates, private communication. 12 Piette and Anderson, J . Chem. Physics, 1959, 30, 899. 13 Alexander, J. Chem. Physics, 1962, 37, 971. Kurland, Rubin and Wise, J. Chem. Physics, l4 Novak and Whalley, Cad. J. Chem., 1958, 36, 1116. l5 Rassat, Jefford, Lehn and Waegell, Tetrahedron Letters, 1964, 233. 16 Anderson, J. E., unpublished results. l7 Barbier, Delmau and Ranft, Tetrahedron Letters, 1964, 3339, and references therein. 18 Hendrickson, J . Amer. Chem. Soc., 1961, 84, 4537. Simmons and Williams, J. Amer. Chem. l9 Lide, J. Chern. Physics, 1960, 33, 1514. 20 Kasai and Myers, J . Chem. Physics, 1959, 30, 1096. 21 Allinger and Freiberg, J. Amer. Chem. SOC., 1960, 82, 2393. Johnson, Bauer, Margrave, 22 Goaman and Grant, Tetrahedron Letters, 1963, 1531. 23 Brown, Katritzky and Waring, Proc. Chem. SOC., 1964, 257. 24 Lide, J. Chem. Physics, 1958, 29, 1426; 1960, 33, 1519. 25 Allerhand, Chen and Gutowsky, J . Chem. Physics, 1965, 42, 3010. 1964,40, 2426. SOC., 1964, 86, 3222. Frisch, Dreger and Hubbard, J. Amer. Chem. SOC., 1961, 83, 606.

ISSN:0014-7672    

DOI:10.1039/TF9666200039

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Vibrational-Rotational-Translational Energy Exchange in Some Polyatomic Molecules BY R. MOLMES, G. R. JONES AND R. LAWRENCE" Dept.of Electrical Engineering and Electronics, University of Liverpool, Liverpool 3 Received 5th July 1965 An investigation of vibrational-translational and rotational-translational energy transfer in n-butane, n-pentane, n-hexane, cyclopentane and neopentane through ultrasonic dispersion and absorption measurements at 29S.2"K and in the frequency/pressure range 10 to 5000 Mc/sec atm is reported. The measured vibrational relaxation times are for n-butane, 1.30 x 10-9 sec atm, for n-pentane, 1-14 x 10-9 sec atm, for n-hexane, 1.23 x 10-9 sec atm, for cyclopentane, 1-93 x 10-9 sec atm and for neopentane, 4-35 x 10-9 sec atm. The results for the normal paraffins are con- sistent with the assumption that rotational equilibrium is achieved as efficiently as translational equilibrium, but for cyclopentane the rotational collision number is 2.4 collisions and for neo- pentane 3.7 collisions.These results are discussed in the light of simple classical and quantum- mechanical theories of molecular energy transfer. In a previous paper 1 measurements in a series of polyatomic gases were reported in which the purpose of the investigations was to test various theories of sound propagation at high frequency/pressure (f/p) ratios. It was found that equations developed by Greenspan 2 9 3 allowed the viscothermal effects to be calculated and the thermal relaxation contributions to be extracted from the measured constants. In the present report, these results are used to analyze investigations of vibrational and rota- tional energy transfer in a series of molecules having very low lying vibrational energy levels.The energy exchange processes are expected to be very efficient, but few experimental data are available. n-Butane, n-hexane and neopentane have been investigated by Lambert and Salter 4 who found no dispersion in the velocity of sound at the highest f/p available with their apparatus, while for n-hexane Klose 5 claims to have detected the beginnings of a dispersion curve at 70 Mc/sec atm and deduced a relaxation time of 0.65 x 10-8 sec at 1 atm and 308°K. Since the lowest vibrational mode of n-hexane is a CH2 torsion of approximately 9 61 cm-1 this seems much too long. Measurements have therefore been made in n-butane, n-pentane and n-hexane to investigate the efficiency of vibrational-translational energy exchange as the length of the carbon chain increases and as the freqilency of the lowest torsional mode decreases.Measurements have also been made in cyclopentane and neopentane for comparison with the normal paraffins. It has been suggested that " wrestling collisions " may occur for chain molecules 6 which would increase the efficiency of energy transfer. This suggestion was based on measurements of the efficiency of some of the molecules investigated here in de-exciting ethylene but it seems preferable to investigate self- collisions between the molecules to see if there are additional factors facilitating energy exchange. For the chain molecules it is expected that the rotational modes will be equili- brated about as efficiently as translation but for cyclopentane and neopentane calcula- tions indicate that an appreciable number of collisons are necessary for rotational equilibrium to be established. * now in the Physics Department, The College of Technology, Liverpool. 46R.HOLMES, G . R. JONES AND R. LAWRENCE 47 EXPERIMENTAL The method of investigation was as previously described by Holmes, Jones and Pusat.1 Sound propagaion constants were measured in the f/p range 10 to 5000 Mc/sec atm using a pulse technique and solid dielectric transducers at 100, 175 and 300 kclsec atm. All the gas samples were obtained from the National Chemical Laboratory and table 1 in- dicates the stated purity and probable impurity. No attempt at further purification was made. TABLE l.-G~s PURITY AND PROBABLE IMPURITY gas n-but ane n-pentane n-hexane cyclopent ane neopentane purity, mole % probable impurity 99.97 0.03 % isobutane 99.98 isopentane 99.96 methyl cyclopentane 99-95 straight chain C5 saturated hydrocarbons 99-88 n-pent ane THEORY Many of the measurements were taken in a region of f/p where viscothermal relaxation occurs. The viscothermal absorption and dispersion were calculated as described by Holmes, Jones and Pusat 1 and the thermal relaxation contributions to the measured absorption and dispersion were extracted using the equations :2 were a is the amplitude absorption coefficient, V is the velocity of sound, VO is the velocity of sound at very low f/p, avt is the viscothermal absorption, atr is the thermal relaxation absorption, V&/ Yo is the viscothermal dispersion, Vtr/ Vo is the thermal relaxation dispersion and A0 is the sound wavelength at very low f/p.For all the gases investigated the measurements could be fitted to relaxation curves assuming that all the vibrational specific heat relaxed with a single relaxation time. For the normal paraffins it was assumed that 2,. (= Nzr, where N is the total number of collisions per second and 7,. is the rotational relaxation time) = 1-3 collisions in extracting the vibrational contribution to the thermal relaxation absorption and dispersion. For cyclopentane and neopentane there was experimental evidence of larger values of Zr and the measurements were used to estimate z,.. It was assumed that the vibrations and rotations are excited independently so that the equations for parallel excitation (see, e.g., Herzfeld and Litovitz 7) could be used to find a value of zv.A preliminary analysis was carried out using the low frequency absorption. At low frequency A = a;l= (2.n2R/CpCv)(C,z,p + C,z,p) f / p , where Cu is the total vibrational specific heat, Cr is the rotational specific heat, C p and CV are the molar specific heats at constant pressure and volume respectively, zw is the vibrational relaxation time and zr is the rotational relaxation time. Assuming a value for Zr = 1.3, a value of zrp and hence a value for zvp was calculated. This value was adjusted to give the best fit to all the experimental data. For cyclopentane and neo- pentane it was necessary to assume larger values for 2,. to get a good fit at high f/p.48 VIBRATIONAL-TRANSLATIONAL ENERGY E X C H A N G E RESULTS Fig.1 and 2 show the total relaxation absorption and dispersion for n-pentane. Fig. 3 shows calculated thermal relaxation absorption curves for neopentane for a f l p , Mc/sec atm sorption ; 4, rotational absorption ; circles, experimental points. FIG. 1 .-n-Pentane 25°C : 1 , vibrational absorption ; 2, viscothermal absorption ; 3, total ab- f / p , Mclsec atm sion ; 4, rotational dispersion ; circles, experimental points. FIG. 2.-n-Pentane 25°C : 1 , viscothermal dispersion ; 2, vibrational dispersion ; 3, total disper-R. HOLMES, G . R. JONES AND R . LAWRENCE 49 series of values of zrp keeping z,p constant. z,p determines the lower f/p portion of the curve, the effect of varying z,p being small in this region.zrp determines the higher f/p portion of the curve. Hence it is possible to fix the value of z,p from the lower f/p measurements and adjust zrp to get a good fit at the higher f/p. Although the x f/p, Mc/sec atm FIG. 3.-neoPentane 25°C : calculated thermal relaxation absorption with various assumed values of 2,. 1, Zr = 1.3 ; 2, Zr = 2.5 ; 3, Zr = 3.7 ; 4, 2 r = 4.7 ; circles, expt. points. flp, Mc/sec atm FIG. 4.--cycloPentane 25°C : calculated thermal relaxation absorption with various assumed values of Z,. 1, Zr = 1.3 ; 2, Zr = 1.9 ; 3, Zr = 2 7 ; 4, Zr = 3-8 ; circles, expt. points. scatter is considerable at high f/p, a value of 2,. = 1-3 does not fit the measurements. A similar analysis was carried out for cyclopentane as shown in fig.4. Table 2 shows the value of z,p which give the best fit with both absorption and dispersion. Thermo- dynamic and transport data used in the calculations are given in table 3. TABLE 2.-vIBRATIONAL RELAXATION TIMES gas r,p, 109 sec atm n-but ane 1 630 n-pent ane 1.14 n-hexane 1.23 cyclopentane 1 -93 neopen tane 4.3550 VIBRATIONAL-TRANSLATIONAL ENERGY EXCHANGE TABLE 3 .-THERMODYNAMIC AND TRANSPORT DATA gas CPIR q 106 poise K, 106 cal cm-1 sec-1 "C-1 n-butane 11-65 0, by h 74.9 c, 4 e 38.0 c, f. g n-hexane 17.212 h , j , X: 64.6 c, e, 33.7 c, cyclopentane 10.192 'n* 75.0 ' 9 O 26.65 4 neopent ane 14.629 P 73.9 38.0 4 n-pentane 14.367 h, 4.i 68.3 Cy 36.0 C9.C a Templeton and Davies, J. Amer. Chem. SOC., 1944, 66,2033. b Dailey and Felsing, J. Amer. Chem.Soc., 1943, 65, 44. C Lambert, Cotton, Pailthorpe, Robinson, Scrivins, Vale and Young, Proc. Roy. SOC. A , d Wobser and Miiller, Kolloid Beihfte, 1941, 52, 165. e Titani, Bull. Chem. SOC. Japan, 1930, 5, 98. f Smith, Durbin and Kobayashi, J. Chem. Eng. Data, 1960, 5, 3 16. h Person and Pimentel, J. Amer. Chem. SOC., 1953, 75, 532. i Pitzer, J . Amer. Chem. SOC., 1941, 63, 2413. Eucken and Starstedt, 2. physik. Chem. B, 1941, 50, 143. k Waddington and Douslin, J. Amer. Chem. Soc., 1947, 69,2275. Craven and Lambert, Proc. Roy. SOC. A , 1951,205,439. m Spitzer and Pitzer, J. Amer. Chem. Soc., 1946, 68, 2537. n McCullough, Pennington, Smith, Hossenlopp and Waddington, J. Amer. Chem. SOC., 1959, 0 McCoubrey and Singh, J. Physic. Chem., 1963, 67, 518. P Pitzer and Kilpatrick, Chem.Rev., 1946, 39, 435. 4 calculated from viscosity using a modified Eucken relation, Mason and Monchick, J. Chem. 1955,231, 280. Mann and Dickins, Proc. Roy. SOC. A , 1931, 134,77. 81, 5880. Physics, 1962, 36, 1622. DISCUSSION In interpreting experimental data it is usual to assume a classical series model in which energy exchange between modes is governed by a single relaxation time 212, where 1 refers to the lowest mode and 2 to all the others collectively, and further that z12< 21 where z1 is the relaxation time of the lowest mode. In this case where C1 is the specific heat contribution of the lowest mode. Physically, because of the additional energy which has to enter a molecule through the lowest mode, the effective (observed) relaxation time is increased by the factor C,/Cl.While it is known that this model is inaccurate it does allow comparisons to be made between different molecules. Calculations by Tanczos 8 indicate that the true value of 2 1 0 (= l/Plo(l), where Plo(1) is the probability per collision of a 1-0 transition in the lowest mode) is closer to 71 = (Cl/CV)ZV, than 210 = Nz,C1/C,( 1 - exp (- hv/kT)) 210 = Nz,(l - exp (- hv/kT)), in which no allowance has been made for the additional energy flow through the lowest mode. These calculations also show that the value of 210 obtained from eqn. (1) will be too small. To estimate 210 from eqn. (I), the fundamental frequency and specific heat contribution of the lowest mode are required. The normal paraffins have lowest modes which are CH2 torsions while that of neopentane is a CH3 torsion, all of which are inactive in infra-red and Raman spectra.For the lowest torsional modes of the n-paraffins we have had to rely on the calculations of Schachtschneider and Snyder 9R . HOLMES, G. R . JONES A N D R . LAWRENCE 51 who have performed a vibrational analysis of the n-paraffins and calculated the torsional frequencies from force constants deduced from the observed spectra. The specific heat contributions were estimated from the equations developed by Pitzer 10 for calculating the thermodynamic properties of the n-paraffins and the tables cal- culated by Person and Pimentel.11 As a first approximation the contribution of the lowest mode was calculated by dividing the total torsional mode contribution by the number of torsional modes.For neopentane the four torsional modes split into a singly degenerate mode and a triply degenerate mode but they are inactive and their frequencies have not been calculated. Hence an estimate of the frequency of the lowest mode (assumed singly degenerate) was made. Calculations were made with II = 200 cm-1 and 300 cm-1. The specific heat contribution of the lowest mode was assumed to be one quarter of the total contribution of the torsional modes. The specific heat of the remaining vibra- tions was calculated from the assignment of Schachtschneider and Snyder 9 and the total specific heat calculated by Pitzer and Kilpatrick.12 First, the assignment of Sverdlov and Prokof’eva,l3 which assumes a plane ring structure was used. According to this assignment the lowest mode is doubly degenerate at 288 cm-1.The specific heat of the lowest mode was calculated by subtracting the contribution of the other vibrations from the total vibrational specific heat. This was calculated from a value of Cp, extrapolated from the measurements of Spitzer and Pitzer.14 If the assignment of Miller and Innskeep 15 is used, which assumes a puckered ring structure, the lowest mode splits into two, one at 207 cm-1 and the other at 288 cm-1. An alternative value of 210 was calculated on this basis. Table 4 gives the details of the calculations. For cyclopentane, two calculations were made. TABLE 4.-DETAILS OF THE CALCULATIONS OF 210 gas v, cm-1 n-butane 102 n-pen t ane 88 n-hexane 61 neopentane 200 300 cyclopentane 288 207 c1 lR 1.35 1.31 1.31 -953 -953 -756 1.33 CvIR 7.65 10.76 13.2 10.63 10.63 6.19 6.19 N 10-10 1 -73 1.74 1.99 1.75 1 -75 1.72 1 -72 2 1 0 1.6 0.88 0.66 4.2 5.2 5.3 2.6 The values of 210 behave in the expected manner in that 210 becomes smaller as the lowest mode decreases in frequency, and the more compact cyclo- and neo-pentanes are less easily excited than n-pentane.The 2 1 0 values are too low since, on physical grounds, values less than 1.3 collisions (the number of collisions to reach translational equilibrium) are inadmissible. It is to be expected that a complex molecule like n-hexane will achieve vibrational equilibrium almost as efficiently as translational equilibrium because of its very low lying torsional mode. A value of Zlo close to 1.3 collisions is therefore expected while the simple classical series model gives a value approximately one half of this.This difference is probably due to the inadequacy of the model. Other factors which would increase the probability of energy transfer, e.g., “wrestling collisions” in which the energy levels of the vibrations become smeared in collisions or because multiple impacts occur between the various parts of the collision partners because of coiling during a collision, must therefore be of only small importance. The measurements in the ethylene mixtures by McGrath and Ubbelohde 6 have been re-analyzed by Cottrell and McCoubrey.16 This analysis shows that neo- pentane and cyclopentane are approximately equally effective in de-exciting ethylene52 VIBRATIONAL-TRANSLATIONAL ENERGY E X C H A N G E and n-butane, n-pentane and n-hexane are progressively more efficient.They have interpreted this in terms of vibration-vibration transfer. It is seen that the efficiencies of the additives closely follow their efficiencies in self-collisions. An attempt was made to analyze the measurements in terms of a quantum mechan- ical series process using the equations developed by Schwartz, Slawsky and Herzfeld 17 and Tanczos.8 The velocity and absorption may be written where zt are experimentally observable relaxation times and Di are relaxation con- stants related to the vibrational specific heats. In the analysis it was assumed that only two transitions are of importance, Plo(1) and P; :(I7 2>, where Plo(1) is the pro- bability of de-excitation of the first level of the lowest mode per collision and f‘; : (1,2) is the probability of de-excitation of the first level of the second mode with simultaneous excitation of the first level of the lowest mode.Further, the effective specific heat of the second mode was assumed to be the total vibrational specific heat less that of the first mode. Calculations of z1, 72, D1 and D2 were made using a value of NPlo(l) = 2-02 x 1010 (i.e.7 the value calculated assuming the classical series model) and for various ratios of P: h(1, 2)/Plo(l), the results being tabulated in table 4. TABLE 5.-RELAXATION PARAMETERS r l p , 1011 sec atm rzp, 1011 sec atm 5.76 2.28 6.35 1.03 6-59 0.399 6.66 0,197 6.69 0.098 6-71 0-039 6.72 0.0196 D1 0.259 - 0.208 0.194 0.190 0.189 0.188 0.187 D2 -0.018 0.033 0.047 0-051 0.052 0.053 0.054 The model predicts double relaxation with an appreciable relaxation constant 0 2 even when Py (1,2)/Plo(l) is large ; this is in conflict with the experimental results which give a single relaxation time involving all the vibrational specific heat.Accord- ing to Stretton,lg the model fails because in a full analysis involving all possible transitions, many transition probabilities are comparable with Plo( 1) and this results in only a single observable relaxation time involving all the specific heat. From table 5, zlp is seen to be constant at 6.5 x 10-11 sec atm which is approximately one quarter of the experimentally observed relaxation time of 2.54 x 10-10 sec atm. To bring these two into agreement, Plo(1) N must be reduced by a factor of 4 and hence 210 is increased to 2.5 collisions.Calculations of rotational collision numbers were carried out using the theory for rough spheres developed by Wang Chang and Uhlenbeck 19 and Sather and Dahler.20 For spherical molecules where b = I/ma2; I is one of the principal moments of inertia, 2m is the mass of the molecule and a is the molecular diameter. [ is a measure of the roughness of the sphere and equals 1 for perfectly rough spheres and 0 for perfectly smooth spheres. Hence for < = 1, a minimum value of 2,. is obtained. neoPentane has a symmetrical mass distribution and may be treated as a rough sphere. Cyclopentane is planar but 2, = 3(1+2b)2/8cbR . HOLMES, G . R . JONES AND R . LAWRENCE 53 its principal moments of inertia differ by only a factor of 2 so that a rough calculation was made treating this as a rough sphere also and using the geometric mean of the moments of inertia.The values of the parameters used in the calculations are given in table 6. Values for a were calculated from the viscosities assuming a spherical model. TABLE 6.-DETAILS OF THE ROTATIONAL RELAXATION CALCULATIONS gas I, 1040 g cmz a. A Z , (calc.) Z , (expt.) neopentane 188-8 7.28 7.9 3.7 h0.5 cyclopentane 158.3 7.17 8.7 2.4 fO.5 These results may be compared with those previously obtained in methane, tetradeuteromethane and cyclopropane.1 For these three molecules the ratio of Z,(calc.)/Zr(expt.) ranged from 1.5 for methane, 1.7 for tetradeuteromethane to 2.1 for cyclopropane. The present results for neopentane and cyclopentane are in agreement with these in that the model always predicts a more inefficient process than is found experiment ally.Rotational-translational energy exchange is expected to be very efficient in the n-paraffins. According to Sather and Dahler 20 the efficiency of energy exchange for spherocylinders (a possible model for the n-paraffins) depends mainly on a parameter a = rnL2/8(111213)*, where m is the mass of the molecule, L is the length of the cylinder and I1, I2, and 1 3 are the principal moments of inertia. For ethylene the authors (Holmes, Jones and Pusat 1) calculated a = 0-59 and hence 2,. = 3.5 collisions. For the normal paraffins, mL2 increases more rapidly than (IlI213)*, hence a is increased and Z, is smaller than for ethylene. Values of 2,. less than 2.5 collisions are expected since in the theory attractive forces are neglected and the spherocylinders are treated as perfectly smooth. Further, the theory is only valid if a (= radius of the spherocylinder cap)$L (i.e., the molecules are almost spherical) and heme multiple impacts may be neglected. For the n-paraffins, L> a so the possibility of multiple impacts can no longer be neglected and these would lead to smaller Z,. . For large a, 2,. tends to 2-5 collisions. 1 Holmes, Jones and Pusat, Trans. Farday SOC., 1964, 60, 1220. 2 Greenspan, J. Acoust. SOC. Amer., 1954, 26, 70. 3 Greenspan, J. Acoust. SOC. Amer., 1959, 31, 155. 4 Lambert and Salter, Proc. Roy. SOC. A , 1959, 253, 277. 5 Klose, J. Acoust. SOC. Amer., 1958, 30, 605. 6 McGrath and Ubbelohde, Proc. Roy. SOC. A, 1954, 227, 1. 7 Herzfeld and Litovitz, Absorption and Dispersion of Ultrasonic Waves (Academic Press, New 8 Tanczos, J. Chem. Physics, 1956, 25,439. 9 Schachtschneider and Snyder, Spectrochim. Acta, 1963, 19, 117. 10 Pitzer, J. Chem. Physics, 1940, 8, 711. 11 Person and Pimentel, J. Atner. Chem. SOC., 1953, 75, 532. 12 Pitzer and Kilpatrick, Chem. Rev., 1946, 39, 435. 13 Sverdlov and Prokof’eva, Optics and Spectr., 1959, 7, 363. 14 Spitzes and Pitzer, J. Amer. Chem. Soc., 1946, 68, 2537. 15 Miller and Tnnskeep, J. Chem. Physics, 1950, 18, 1519. 16 Cottrell and McCoubrey, MoIeczdar Energy Transfer in Gases (Butterworths, London, 1961). 17 Schwartz, Slawsky and Herzfeld, J. Chem. Physics, 1952, 20, 1591. 18 Stretton, Thesis (Oxford, 1964). 19 Wang Chang and Uhlenbeck (University of Michigan), 1951, Report CM-681. 20 Sather and Dahler, J. Chem. Physics, 1961, 35, 2029. York, 1959), p. 102.

ISSN:0014-7672    

DOI:10.1039/TF9666200046

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Viscosities of the Inert Gases BY M. RIGBY AND E. B. SMITH Physical Chemistry Laboratory, Oxford University Received 3rd June, 1965 The viscosities of argon, krypton and xenon have been measured, relative to that of nitrogen over the temperature range 293-972°K. A discrepancy between the results for krypton and those reported by a previous worker was observed. The new results are consistent with the principle of corresponding states. An important generalization in the study of intermolecular forces is the prin- ciple of corresponding states.1 If a number of substances adhere to this principle it may be concluded that their intermolecular potential energy may be described in terms of one function involving only two parameters characteristic of each sub- stance.It is therefore important to discover with what accuracy the principle is obeyed. The second virial coefficients of the inert gases may be shown to follow the principle within the accuracy of the experimental determination 2 but applica- tions to the transport properties have been less successful. In particular, the deter- mination by Clifton3 of the viscosity of krypton cannot be reconciled with the viscosities of argon and xenon to the degree expected from the probable accuracy of the experimental data. It seemed desirable therefore to carry out measurements of the viscosities of argon, krypton and xenon over an extended temperature range, and to examine critically the degree to which the data were in agreement with the principle of corresponding states.EXPERIMENTAL The viscosities were determined in the temperature range 293-972°K by a capillary flow method. Measurements were made of the time for the pressure in a standard globe and connections to drop from about 26 to 12 cm Hg as the gas flowed through a capillary maintained at a known temperature. Values of the viscosity of the gas were obtained by comparing the times with those found for a gas of known viscosity under identical conditions. The gas was initially contained in a 1 1. vessel thermostatted in a water bath at 25 10.1 "C. The pressure drop in the vessel was followed by means of a mercury manometer in which were set 3 platinum pointers at positions corresponding to pressures of 26, 19 and 12 cm Hg.Two capillaries were used. The first was constructed of a 150 cm length of Pyrex capillary tubing of int. diam. 0.04 cm wound in a close helix of 6 cm diam., outside which was a helix of wide bore (0.8 cm int. diam.) tubing, 150 cm long, acting as a heat exchanger. The second capillary was of silica, 200 cm long and of 0.040 cm int. diam. wound in a close helix of 10 cin diam., within which was a helix of 0.5 cm int. diam. tubing 150 cm in length. The capillaries were placed in a furnace thermostatted to il"C, and the furnace tem- perature was measured using a calibrated Pt/Pt-Rh thermocouple. The gas was passed through the capillary into a 5 1. globe which was evacuated before each experiment. In most experinients two values of the viscosity were obtained, by comparing the flow times for the pressure drops of 26-19 crn and 26-12 cm Hg.At the highest temperatures, when the times of flow became inconveniently long, only the first pressure range was used. The times of flow varied from 29 min to 4 h. The flow times were reproducible to better 54ni. RIGBY AND E . B . SMITH 55 than 0.1 % and the values of the viscosity derived from measurements over different pressure ranges were consistent to better than 0.3 %. Standard slip corrections were applied4 and amounted to not more than 1 ”/, in the final values. No correction was made for curved pipe flow as the application of White’s formula 5 indicated that this correction was negligible. Nitrogen was used as the reference gas, the values of its viscosity being taken from a sinooth curve based on the determinations of previous workers.6-9 The data of Trautz et al.were increased by 0.6 % to correct for the low value of air used in their calibrations,7 a procedure which was also applied to their results for argon and xenon considered sub- sequenily. The results obtained by Kestin 7 above 450”K, where they deviate systematically from those of other workers, have been neglected. The remaining determinations between 273 and 1000°K were all within 0.5 % of the smoothed values. In general, values in the lower temperature range were obtained using the Pyrex capillary and those at the higher temperatures using the silica capillary. At a number of tem- peratures viscosities were measured using both capillaries and the results were found to be consistent, the differences being less than 0.4 %.Runs repeated at intervals of many hours showed that the average temperature of the capillary varied by less than 0.3”. ?he chief source of error probably lies in the uncertainties in the viscosity of nitrogen, but the results are believed to be in error by less than 1 %. The nitrogen used was British Oxygen Company “ white spot ” nitrogen dried over P2O5. Mass-spectrographic analysis indicated the presence of less than 0.4 % impurity. Argon from the same source was dried over P2O5. Mass-spectrographic analysis set the same lower limit on the purity. The molecular weight of the gas, determined using a density balance, was within 0.05 % of that of pure argon. The krypton, provided by the same company, was stated to be better than 99 % pure and the mass spectrometer confirmed that the impurities were less than 0-3 %.Each sample was frozen in liquid air and pumped lightly before being passed into the viscometer. The xenon, from the British Oxygen Company, was stated to be better than 99 % pure. Mass-spectrographic analysis indicated less than 0.2 % krypton. Each sample was frozen and pumped before use. RESULTS AND DISCUSSION The viscosities obtained are given in table 1, together with the reference datz for nitrogen. In fig. 1 the results for argon and xenon are compared with those reported by previous workers.10-15 The data for argon are in excellent agreement with those of other workers over the whole temperature range. The values we TABLE TER VISCOSITIES OF THE INERT GASES ( p poise) T(OK) 293 363 453 505 553 575 610 654 678 725 775 821 855 921 972 reference N2 175.5 205.7 240-0 258.4 275.3 282.5 294.3 308.4 315.6 329.0 342.5 355.0 364.1 380.7 393.4 Ar 221.3 264.2 311.6 338.4 361.6 371-5 387.7 407.5 41 8.0 436.3 455.7 472.5 483.5 507.6 526.7 Kr 249.8 301 *2 361.0 393.4 423.9 438-8 456.8 480.1 494.0 5 18.9 539.6 564.0 579-1 608.2 630.2 Xe 227.2 278.8 336-6 370.9 41 5-9 438.1 462.0 475.7 502.3 525-6 548.4 563-6 595-1 620-2 -56 6 0 0 5 0 0 h .d 8 W h 0 a 400- E' 300 3 2 0 0 I I I I I I I 0 t 3 - - 0 0 0 A - - 0 A Es n 0 ,cn 0 A 0 o > c ) o n - n @ 2 Q A X X o h - - 0 LF xF - I I I I I I - I 3 0 0 500 700 900 T°K FIG.2.-Viscosity of krypton. U, this work : 0. ref.(3)M. RIGBY AND E. B . SMITH 57 report for xenon are also in good agreement with the corrected determinations of Trautz and Heberling 13 up to their highest temperature and with the values given by Rankine 14 and Thornton.15 The data for krypton are illustrated in fig. 2. They are in good agreement with the data of Nasini,l6 Rankine and Thornton at lower temperatures. In view of the excellent agreement between our results and those of other workers for argon and xenon it seems probable that the results of Clifton 3 are in error by as much as 4 %. A - 8 B A I 2 T/TB FIG. 3.-Reduced viscosities of argon, krypton and xenon. A, argon (this work) ; A, argon 9-12 ; 0 , krypton (this work) ; 0, krypton 3 ~ 1 5 ; m, xenon (this work) ; 0, xenon.13~ 15 In order to apply the principle of corresponding states it is necessary to define suitable characteristic parameters for each substance.The use of critical volumes and temperatures has been criticized because the intermolecular potential energy may not be pairwise additive. This could lead to irregularities in behaviour at the critical point. The use of Boyle temperatures TB and Boyle volumes, VB = T(dB/dT)T=TB, has a number of advantages.17~ 18 Thus, for a given potential function the calculated second virial coefficients may be directly related to the cor- responding experimental determinations. Furthermore, the uncertainties that may arise from non-pairwise contributions to the energy are no longer relevant. We have used the Boyle temperature and the magnitude of the second virial coefficient at T = O-~TB,(B~).The latter characteristic volume, having all the advantages of the Boyle volume, is more readily determined (as it does not require numerical differentiation of the experimental data). The values of these parameters for argon,58 VISCOSITIES OF THE INERT GASES krypton and xenon are given in table 2. They give an excellent corresponding states plot for the second virial coefficients of these gases. The reduced viscosities, qBt(MT)-* for argon, krypton and xenon as a function of reduced temperature are illustrated in fig. 3. A smooth corresponding TABLE 2.-REDUCTION PARAMETERS Ar Kr Xe =B, OK B:, cm3/mole 410 18.3 570 22.7 775 29.7 * B o = -&i"=0.7TB) states curve is obtained with points scattered within the estimated experimental errors.The results of Clifton for krypton lie well below the curve. The evidence presented suggests that these results are too low and that the viscosities of the inert gases follow the principle of corresponding states as do the second virial coefficients. M.R. thanks the S.R.C. for the award of a Research Studentship. 1 Pitzer, J. Chem. Physics, 1939, 7, 583. 2 Guggenheim, Rev. Pure Appl. Chem. (Austral.), 1953, 3, 1. 3 Clifton, J. Chem. Physics, 1963, 38, 1123. 4 Partington, Physical Chemistry (Longmans, London, 1949), vol. 1, p. 885. 5 White, Proc. Roy. Soc. A , 1929, 123, 645. 6 Johnston and McLoskey, J. Physic. Chem., 1940,44, 1038. 7 Kestin and Whitelaw, Physica, 1963, 29, 335. *Trautz and Zink, Ann. Physik, 1930, 7 , 427. Trautz and Heberling, Ann. Physik, 1931, 10, 155. Trautz and Melster, Ann. Physik, 1930, 7 , 409. Trautz and Baumann, Ann. Physik, 1929, 2, 733. 9 Vasilesco, Ann. Physique, 1945, 20, 292. 10 Johnston and Grilly, J. Physic. Chem., 1942, 46, 948. 11 Trautz and Ludewigs, Ann. Physik, 1929, 3, 409. 12 Trautz and Binkele, Ann. Physik, 1930, 5, 561. 13 Trautz and Heberling, Ann. Physik, 1934,20, 118. 14Rankine, Proc. Roy. Soc. A , 1910, 83, 516. Rankine, Proc. Roy. Soc. A , 1911, 84, 181. 15 Thornton, Proc. Physic. Soc., 1960, 76, 104. 16 Nasini and Rossi, Gazz. chim. ital., 1928, 58,433. 17 Kihara, Rev. Mod. Physics, 1953, 25, 831. 18 Munn, J. Chern. Physics, 1964, 40, 1439.

ISSN:0014-7672    

DOI:10.1039/TF9666200054

出版商:RSC    

年代:1966

数据来源: RSC

摘要:

118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point.These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order.The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No.13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility. The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure.This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13.118 ELECTRICAL THEORY OF ADBORPTTON The writer considers the double layer as consisting of a swface of rigidly fixed atoms under continuous bombardment of positively and negatively charged ions, any particular point on the rigid surface becoming in turn negative, neutral and positive, these conditions arisdg in any order. The observed contact difference is the average effect of these conditions. Where several kinds of atoms are present in the solution the average number of any one of them at the surface will depend on their concentbration, valency and mobility.The variation of contact Werence from negative to neutral and positive was observed with cotton and aluminium sulphate near the neutral point. These variations occurred during the same experiment, the readings being direct measurements of E.1I.F.s developed by filtration under pressure. This point would be covered by putting n2 = 1 and = 2 or 3 in Mukherjee’s equation No. 13. Radiolysis of Gaseous Mixtures of Methane with Argon or Xenon BY R. W. HUMMEL Wantage Research Laboratory (A.E.R.E.), Wantage, Derks. Received 4th June, 1965 Mixtures of CH4 with Ar or Xe have been irradiated with 4 MeV electrons at ambient tem- peratures and atmospheric pressure. Variations of the yields of H2 and low-molecular-weight hydrocarbons with mixture composition are discussed in terms of the reactions of ions and of excited states. Energy transfer from excited Ar atoms to CH4, resulting in methylene radical and molecular H2 formation, appears to account for more than half the enhanced yields of H2 observed in mixtures of Ar and CW4.Charge transfer processes can account for the rest. The variations in the yields of hydrocarbon products are also consistent with this type of energy transfer mechanism Evidence for energy transfer from excited Xe atoms to CH4 is also given. At the beginning of a programme of work on the radiation-induced oxidation of gaseous hydrocarbons, some irradiations of pure CH4 were done in order to have a comparison between yields reported in the literature and those found by us, the latter being based on the N20 dosimeter.1 Our values were similar to those reported by Lampe 2 over a wide range of total doses, but the appearance of liquid products at the highest doses 3 prompted a more detailed investigation involving the addition of rare gases with ionization potentials above and below that of methane. Three papers have appeared on the radiolysis of CH4 in the presence of rare gases. Meisels et aZ.4 carried out radiolyses under conditions where CH4 was a minor component (about 2.5 %) in either Ar or Kr, and Maurin 5 includes a few experi- ments in which Xe or Ar was present as the minor component (12-27 %). Since this work was completed, Ausloos et nZ.6 have reported work on solid mixtures of these substances.Other work on the radiolysis of CH4 has not included the addi- tion of rare gases.7-14 A more complete study of such mixtures seemed worthwhile.EXPERIMENTAL PURIFICATION OF MATERIALS Methane was purified as described earlier,lj but the method was improved slightly by including a 13x molecular sieve trap at -78°C in the purification line to ensure removal of branched chain hydrocarbons. Argon containing not more than 0.05 % impurities was either condensed with liquid N2 and subjected to several thaw-pump cycles and trap- to-trap distillations, or it was first passed through a 50 cm tube containing sodium-coated glass wool. There was no noticeable difference in the results obtained. Xenon, " 99-100 per cent, balance krypton ", was frozen with liquid N2 and pumped on for a short time. 0 2 , " 99.5 per cent or over ", was not further purified.IRRADIATION TECHNIQUE Most of the work reported here was done with the 4 MeV electron beam from a linear accelerator at a dose rate of about 1.6 x 1021 eV min-1 (g CH4)-1. The average volume of the spherical Pyrex bulbs was about 140 cm3. To them were sealed capillary stopcocks via a 15 cm capillary neck to keep the stopcock well out of the radiation zone. A streani of cold water (10-20°C) was played over the bulb during irradiation. A measurement of 5960 RADIOLYSIS OF METHANE the pressure increase in a bulb during irradiation gave a temperature increase of 11"C, occurring in the first 10 sec. All irradiations were done at about atmospheric pressure. DOSIMETRY Bulbs containing pure CH4 were irradiated so as to cause about 0.8 % CH4 decomposi- tion, following which the C2H6 content was measured gas chromatographically. Other work in these laboratories, comparing the c2H6 yield based on N20 dosimetry 1 and the C2H6 yield from T2fCH4 mixtures, had shown that G(C2H6) = 2-00 molecules per 100 eV to within 3 % up to this conversion level.A re-calculation based on more recent evalua- tions of tritium decay data indicate that our best value for G(C2H6) is now 2.10, and this is used here. The rates of energy input into the gas mixtures in other bulbs irradiated during the same experiments were calculated according to their respective electronic stopping powers in MeV cm-1 at 1 MeV (suppl. NBS circ. 577, 1958). In these calculations the stopping powers at 1 MeV were used although the incident electrons have a range of energies below 4 MeV.This is because the ratio (CH4 stopping power)/(rare gas stopping power) decreases with electron energy by only 8 % between 0.4 and 4.0 MeV, so that the arbitrary selection of stopping powers at 1 MeV simplifies the calculations without introducing a significant error. It would be incorrect to use electron densities to calculate the energy deposited when irradiating systems in which the components have significantly different mean atomic numbers and the incident electrons have large ranges compared with the sample dimensions. In Ar + CH4 systems the calculated energy absorption differs signifi- cantly according to the method of calculation used. The linear rate of energy loss by a 1 MeV electron in Ar is about 51 % greater than in CH4, while there is an 80 % difference in energy deposition on the basis of electron densities (at a given temperature and pressure).All the experiments with Ar+CH4 mixtures were done so as to maintain the % decom- position of CH4 (as calculated from the observed yields of C2-C5 products) at 0.1-0-2 % irrespective of the mixture composition. This was possible by varying the irradiation time inversely as the ratio (CH4 electron density)/(total electron density). The conversion level chosen was the minimum at which reasonably accurate analyses for all gaseous pro- ducts could be made over the whole range of mixtures. The same general procedure was followed with Xe+ CH4 mixtures, with the additional assumption (based on the product yields) that only about 25 % of the energy absorbed by the zenon was effective in inducing CH4 decomposition to give gaseous products, i.e., greater doses were needed to give the required amounts of gaseous products than were calculated on the basis of the electron densities of the mixtures. ANALYTICAL METHODS All products were analyzed by gas chromatography; both thermistor and flame ion- ization detectors were used.Calibration factors were obtained using synthetic mixtures with pure CH4 where possible. After irradiation, the gaseous products were not separated from the CH4 or CH4+ rare gas mixture ; the irradiated gas was expanded into a 7 cm3 sample vessel from which the sample was subsequently flushed on to the chromatographic column. However, at the lowest doses, when the amounts of H2 were too small for gas chromatographic analysis, the irradiated sample was frozen at 20°K (liquid H2) and the amount of residual gas deter- mined by BVT.RESULTS AND DISCUSSION HYDROGEN FORMATION I N ARGON + CH4 In pure CH4 the H2 yield was proportional to dose (gamma rays at 3.5 x 1017 eV min-1 g CH4)-1 from 0.1 to 1.0 % CH4 decomposition (assuming G(-CH4) = 8). Irradiations with 4 meV electrons from 0.004 to 4 % CH4 decomposition gave ap- proximately the same yield (G(H2) = 5-7). At higher % decompositions G(H2) decreased, following closely the curve obtained by Lampe.2R. W. HUMMEL 61 The addition of A.r or Xe to CH4 significantly altered G(H2), as illustrated in fig. l.* More H2 was obtained from CH4+Ar mixtures than would have been expected from the complete transfer of energy from Ar to CH4 (to give the same spectrum of processes occurring in pure CH4).The addition of about 1 vol % of 0 2 to pure CH4 reduced G(H2) from 5.7 to 2.7. The same amount of 0 2 added to a 1 : 1 Ar+CH4 mixture reduced G(H2) from 8.0 to 5.0. In both cases AG(H2) was -3.0. The same numerical decrease was obtained with a 3 : 1 Ar+CH4 mixture when 0 2 was added. Thus a greater I I I I - 0 I- - I I I 0 . 2 0 . 4 0.6 0.8 I - stopping power fraction monatomic gas 0 FIG. 1.-Hydrogen yields at constant CH4 % decomposition. 0, argon+ CH4 mixtures ; x , xenon+ C& mixtures % of the H2 is produced by processes unaffected by 0 2 as the Ar content is increased. (The 1 : 1 and 3 : 1 Ar+CH4 mixtures have Ar stopping power fractions of 0-60 and 0.82 respectively.) These results will be discussed initially in terms of ion-molecule reactions.The most important reactions involving ions in pure CH4 at very low conversions are probably the following : CH4m-+CHz +e (A) CH4*+CHi +H+ e (B) CH; +CH4+C2Hf +H2 C2H; +e+C2H4+H CHZ + CH4-+CHf + CH, CHS +e+CH,+H2 (4) CH,f +CH4-+C2Hl +2H2 ( 5 ) * The G values of products obtained from mixtures are calculated using the total energy dis- sipated in the mixtures.62 RADIOLYSIS OF METHANE Kinetic data 16-18 indicate that, in the presence of 1 % 02, reactions of the H atom with CH4 16 or c2& 17 will be negligible compared with the reaction with 02.18 The observed yield of H2, G(H2) = 2.7, is then presumably the result of ionic reactions (l), (4) and (5), and of non-ionic molecular hydrogen formation, e.g., CHz+ CH, + H, The addition of Ar to the CH4+02 mixture increases both the total €32 yield and the non-scavengeable yield without increasing by more than about 5 % the total number of ions produced per unit energy input.(The W values for Ar and CH4 for electrons are 25-5 & 0.3 and 26.8 & 0.4, respectively.19) However, in the presence of Ar the CH:/CH; ratio may be smaller 20 and therefore, if reactions (I), (4) and ( 5 ) are the major sources of non-scavengeable H2, the G value should either de- crease or remain constant depending upon whether CHS disappears by ( 5 ) or (4), respectively. Since G(H2) increases, some other H2 source must exist. (This in- crease in G(H2) argues particularly against an important contribution by reaction (5) in CH4 radiolyses.) If reaction (1) is followed by the sequence C2H,f + CH4-+C3H; + H2 (7) C3H,f +CH4-+C4Hl +H,, etc.(8) more ltq2 per primary ion formed in the As + CH4 + 0 2 system should result from the increased CH:/CHZ ratio. However, although (7) is exothermic and (8) approxim- ately thermoneutral, the major fate of C2Iii is either neutralization 49 21 or, at higher doses, hydride ion transfer.11 The sequence (l), (7), (8) therefore also does not suffice to explain the increase in G(H2) in CH4+02 mixtures when Ar is added. In the absence of 02, where El2 formation by H atom reactions is possible, the change in the CHi/CHl ratio on adding Ar to CH4 is again unlikely to account for the observed rise in G(H2).This can be shown as follows. The yield of H2 from ionic processes such as (l), (4) and (5) is a function of the total yield of ions, of the relative amounts of the major ions, and of the number of IQ2 molecules formed per major ion. Since the ions may undergo other reactions not leading to H2 formation, a probability factor P must be associated with each ion. These con- siderations are collected in the equation 3 G(Hz)i,ni, = C;(ions) 1 ( I z I P ) ~ i = 1 Here G(ions) = lOO/W = 3.4 and the three major ions considered are CH;, CHZ and CH;, which are formed in the relative amounts 11, 12 and 13, respectively. In pure CH4, 11 = 0.35 and I 2 + 1 3 = 0.65. The probability factors Pi are taken to be the same for each ion under all conditions. A value for P can be derived from previous work 14 in which it was suggested that G(C2H4) from CH4 in the presence of 02, equal to 0-65, resulted from the occurrence of reaction (6).Under these conditions, G(H2)totai = 2.7, SO that G(H2)ionic =I 2.7 -0.65 = 2-05. Consequently, since H atom reactions to give H2 are suppressed, n1 =; 1. Also n3 and, on the basis of the present and other 11 work which indicates reaction ( 5 ) is unimportant, n2 = 1. Therefore from which P = 0.6. In pure CH4, G(H2)ionic = 2.05 = (3.4)(0.35 + 0.65)Y G(H,)tota, = G(H2)ionic + G(H2h + G(H~)H~ where G(H& is the yield from reaction (6) and G(H2)15 comprises not only theR. W. HUMMEL 63 H2 resulting from CH~---~M.+CH~+H, for which 14 G(CH3) = 2.0 and conse- quently G(H& = 1.0, but also the H2 resulting from (B) and (2), for which Consequently in agreement with experiment.where 20 I1 = 0-54 and 12 + 13 = 0.46, G(H2)B = 3-41, +0.6(3.4)11 = 1.9. G(H2)total = 2.0 + 0.7 + (1 -0 + 1 *9) = 5.6, Finally, in the presence of Ar (Ar/CH4 = 10) G(H2)ionic = (0.6)(3.4)(0.54+0.46) = 2.0; G(H2)M = 0.7; G(H2)B = (3*4)(0.54) + (0*6)(3*4)(0*54) = 2.9; G(H2), = 1.0 and therefore G(H2)total = 6.6. This final summation assumes that in the presence of Ar energy is transferred from Ar to CH4 to produce molecular H2 (reaction (6)) and H atoms (via CH4-t CH3+H) in amounts exactly equivalent to that which would have been produced by direct radiolysis of CH4. The effect of altering the CH,+/CE€$ ratio alone is therefore to change G(H2)total by a maximum of one unit, or less than half the total observed change.The increase in G(H2) cannot be due to energy transfer from the lower excited Ar* levels at about 11.6 eV to give ionized CH4, since the ionization potential of CH4 is about 1-4 eV higher than these Ar* levels. Ionic processes therefore do not appear to be responsible for more than 45 % of the enhanced values of G(H2) in mixtures of Ar and CH4. Energy transfer from ArZk to CH4 can account for the results if the transfer leads directly to H2 formation, e.g., by reaction (6). The lowest excited states of Ar are triplets, but since the ground state of CH4 is a singlet ( ~ A I ) , the methylene radical would have to be a triplet if the spin conservation rule applies, i.e., Ar(3P,) + CH4(1Al)+CH4(3T2) +Ar('S0) CH4(3?'2)--+CH,(3Z~)+H2(1Cgf).However, it has been suggested22 that the most abundant excited state of the As atom in a system exposed to electronic bombardment is the 1P1 level at 11.82 eV. This would lead to singlet methylene formation. Ar('P,) + CH4('Al)+CH4(1 T2) fAr(' So) CH4(1?'2)+CH2(1A,)+H2('C,+). It is therefore suggested that both triplet and singlet excited Ar atoms transfer energy to CH4 to give molecular H2. The transfer must be efficient, relative to molecular H2 formation by direct excitation of CH4 by electrons, in order for G(H2) to increase in the presence of Ar. The reason for this efficiency may merely be statistical ; energy transfer from a high energy electron to CH4 can produce a variety of modes of decomposition or means of energy dissipation, whereas energy transfer from Ar* may give H2 exclusively.Only a part of the increase in G(H2) may arise directly from reaction (6). Subsequent addition of CH2 to CH4 may account for the rest via the exothermic reactions (9)-( 12) : CH2 + CH4-+C,H: (9) C2Hg + 2CH3 (10) C,Hg+C,H,+H, (11) C2HE-+ C2H2 + 2H2 (12)64 RADIOLYSIS OF METHANE The mode of C2Hg decomposition may depend on the multiplicity of the CH2 radical, just as the products of CM2 addition to the double bond of butene-2 are a function of methylene multiplicity.23~ 24 Reactions (9)-(12) have been pos- tulated 149 25-27 to account for results obtained under various conditions of photo- lysis and radiolysis, reactions (lo), (11) or (12) being favoured in accordance with the particular observations. Methylene radicals produced by photolysis of diazo- methane were assumed 27 to react via eqn.(9) and (lo), and no C2H4 was reported among the products. All four of these reactions were required to explain the results of vacuum ultra-violet photolyses of methane,26 presumably because methylene produced by 1236 A photons possesses excess energy. Low 25 and high 14 energy electron irradiations of methane also give ethylene and acetylene, which can be the products of methylene addition to methane. .i stopping power fraction monatomic gas FIG. 2.Ethane and ethylene yields at constant C& % decomposition. 0, argon+ C& mixtures)CZH6 ; x , xenon+C& mixtures 0, argon + CH4 m.ixtures)czH4 A, xenon+ CH4 mixtures The curve for G(H2) in the presence of Ar (fig. 1) shows no tendency to fall at Ar stopping power fractions above 0.8, whereas all the yields of saturated hydro- carbons (fig.2-4) drop appreciably in this region. On the other hand, G(C2H4) increases rapidly at high Ar contents (fig. 2). These results are explicable in terms of the increasing part played by reactions (7)-(9) and (1 1) as the Ar content is increased, and the decreasing contribution due to H atoms, produced by direct radiolysis of CH4, reacting with the C2H4. HIGHER HYDROCARBON FORMATION I N ARGON+ CH4 The variation in G(C2H4) with composition in Ar + CH4 mixtures was attributed above to varying contributions by direct radiolysis of CH4 and by energy transfer from Ar*, and also to H atom scavenging by C2H4 at lower Ar contents. BecauseR. W. HUMMEL oo 0.2 0.4 0 .6 0.0 65 . o I I I I I I I 0 I I I 0.2 0.4 0 . 6 0.8 stopping power fraction monatomic gas 0 FIG. 4.-N- and iso-butane yields at constant C€& % decomposition. 0, argon+ CH4 m i x t u r e ~ ) , - c ~ ~ ~ ~ ; , argon + CH4 x , xenon+CH4 mixtures A, xenon+ CH4 mixtures 366 RADIOLYSIS OF METHANE of H atom scavenging, fig. 2 will not represent the total effect of Ar in increasing G(C2H4) via reaction (1 1). At lower % conversions the curve may be expected to be shifted upwards, especially at low Ar contents. The rapid increase in G(C2H4) at high As levels is reflected not only by the main- tenance of a high G(H2) but by falls in the G values of the saturated hydrocarbons. On the basis of the present arguments, the latter must be due to the lower proba- bility of H atom formation, giving a net reduction in the contributions made by the following reactions : CH4- +CH3 + H (1 3) C2H4 + H- -X2H5 (14) At moderate Ar contents, where G(C2H4) is much increased by reactions (7)-(9) and (ll), and (13) is still appreciable, reactions (14)-(16) can give rise to the ob- served increases in G(C3H8) and G(n-C4Hlo) (fig.3 and 4). Formation of these hydrocarbons by CH2 insertion is unlikely, since formation of C3Hg by CH2 insertion in C2H6 is unimportant 28 in the vacuum ultra-violet photolysis of CH4. The variation of G(iso-C4H10) with composition in Ar + CH4 mixtures does not follow the general pattern in that there is no sign of a pronounced maximum in the curve. The inference is that a different mechanism applies in this case.There is evidence 14 that ~so-C~H~O is formed via the sequence This evidence is (A) from the mixture CH4+ 1 % C2H2, G(C3H6) = 0.7. On the other hand, C3H6 is not obtained from pure CH4, CH4+02, or CH4fC2PI4. (B) From the mixture CH4+ 1 % C3H6, G(iso-C4H10) = 2-0, compared with G = 0.08 and 0.10 from pure CH4 and CH~+CZH~, respectively. Therefore the formation of ~so-C~H~O depends on the occurrence of a reaction such as (12), unlike the other hydrocarbons, whose yields depend on reactions (10) and (11). Reaction (12) is presumably the least important of the three. Alternatively, C2H2 does not have CH2 as a precursor. An alternative route for iso-C4H10 formation, via CH2 addition to propane, is unlikely for the reason mentioned above with respect to C3H8 and n-C4Hlo forma- tion. Similar curves for C3Hs and i-C4H10 would also be expected, contrary to the observations (fig.3, 4). Other experiments, in which either 2.5 % C3Hs or 1.0 % C3H6 was added to pure CH4, gave additional evidence on this point. When C3H8 was added, only a slight increase in G(iso-C4HIO) was observed; when C3H6 was added, a much greater increase in G(iso-C4H10) was obtained, as indicated above. MIXTURES OF XENON A N D METHANE Since I.P. (CH4) = 13.12 eV and the ground state Xe+ ion exists as a doublet (Xe+(2P3) = 12.13, Xe+(W+) = 13.44), charge transfer is only possible from Xe+(2P+). The relative probabilities of ionization to the two levels of the doublet have been studied by mass spectrometry. The results are variable but it appears that theR.W. HUMMEL 61 lower level is most highly populated.29 Even if both levels are assumed to be equally populated, the probability of charge transfer from Xef will be no more than half that from Arf. The thermicities of reactions (21) and (22) indicate that the most abundant ion produced by Xe'(2P+)+CH4-+Xe(1S,)+CH~; AH = -7 kcal, (21) Xe+(2P+)+CH4-+Xe(1So)+CH,f +H; AH = 20 kcal, (22) charge transfer should be CHZ, and this appears to have been borne out experi- mentally.30 The net chemical change resulting from CH,+ reactions will be less than expected from the frequency of (21), owing to exchange with Xe; Whether or not there is a net charge transfer following (21) and (23) is uncertain. Field and Franklin 31 inferred from mass spectrometric data shown in their fig.6 that as the Xe pressure was increased from 0 to 13 p (CH4 pressure about 40 p) the ratio (115 +129)/(117 +116) remained constant, and consequently that there may have been no net charge exchange between Xe+ and CH4. (The argument is based on the exothermicity of (21), which would lead to a predominance of CHZ and its reaction product CH4 in the presence of Xe if the rate of (23) was low.) However, the experimental points on that figure are such that a linear decrease in the ratio is possible, amounting to 10 % as the Xe concentration is raised to 10 %. This would indicate an increase in the CHi/CH$ ratio with increasing Xe content and a net charge transfer from Xe+ to CH4. Charge transfer from Xef to CH4 is there- fore indicated by both theory and experiment to occur to a relatively small extent, giving mostly CH2;.With ionic processes restricted and yet considerable yields of CH4 degradation products observable at high Xe contents (fig. 1-4), energy transfer from the various excited states of Xe must be considered. The two lowest excited states are those corresponding to the resonance wavelengths at 9-6 eV(1Pl) and 8.4 eV(3P1), which must be compared with the continuous CH4 absorption in the ultra-violet 32 be- ginning at about 1455 A (8.5 eV) and with the first intensity maximum at about 1250 A (9.9 eV).33 In addition, excitation potentials for CH4 at 10.2 and 11.8 eV have been found by electron impact 34 and by the trapped-electron method.35 It would therefore appear that electronic excitation of CH4 by transfer from the lowest excited state of Xe at 8-4 eV is unlikely, while transfer from Xe(lP1) at 9.6 eV, although below the excitation potential maximum at about lOeV, is well within the continuous absorption band of CH4 and hence can be envisaged.Energy transfer from Xe(lP1), by analogy with the Ar system, would be expected to cause molecular H2 formation from CH4 as in reaction @a). However, at the same time a rise in G(C2H4) should be observed at high Xe contents; this was not observed (cf. fig. 2). Thus, while energy transfer from Xe to CH4 occurs, and is probably due to Xe* and, in part, to Xe+(2P3), the situation is less clear than the Ar case where Ar* plays a major role. Finally, some indication of a related mechanism for some large fraction of the C2H6 and c3H8 formed in these systems, as well as an illustration of the importance of the relative energy levels of the species involved in determining the spectrum of processes which can occur, can be gained from a consideration of the results shown in fig.5. The C~&/C~HS ratio is the same in pure CH4 and in CH4+Ar and remains constant with increasing dose, but in CH4+Xe, although the ratio appears initially to be the same as in the other systems, with increasing dose it rises rapidly. If a common initial value is assumed, it may be inferred that both Xe(1So)+CH~-+Xe'(2P3)+CH4; AH = -23 kcal. (23)68 RADIOLYSIS OF METHANE C2Hs and C3H8 are produced in a set of related reactions originating, e.g., in reaction (6) and proceeding through (9)-(11) and (13)-(15). The shapes of the lines in fig.5 can be explained on the basis of indiscriminate energy transfer from either Ar or CH4 (in excited or ionized states) to the higher hydrocarbons, due to the fairly I I I I dose, eVx 10-21 FIG. 5 . T h e ratio C&6/C3H8 as a function of dose in pure C& and in 50 vol % mixtures with 0, CH4 ; A, Ar/CH4 ; x , Xe/CH4 0 4 8 I 2 16 argon and xenon. Here 1021 eV corresponds to about 1 % CH4 consumption. large energy excesses for these transfers, whereas with Xe some of the transfers to C2H6 have an energy deficit. Consequently in Xe the C2H6 molecule is relatively stable and tends to accumulate as the radiation dose increases, resulting in an in- creasing C2H6/C3H8 ratio. I am indebted to many colleagues for useful advice and discussions, and especially to Mr. D. Rush who did most of the experimental work. 1 Hearne and Hummel, Radiation Res., 1961, 15, 254. 2 Lampe, J. Amer. Chem. SOC., 1957,79, 1055. 3 Hummel, Nature, 1961, 192, 1178. 4 Meisels, Hamill and Williams, J. Physic. Chem., 1957, 61, 1456. 5 Maurin, J. Chim. Physique, 1962, 59, 15. 6 Ausloos, Rebbert and Lias, J. Chem. Physics, 1965,42, 540. 7 Bogdanov, Rum. J. Physic. Chem., 1960, 34, 496. 8 Mains and Newton, J. Physic. Chem., 1961,65,212. 9 Yang and Manno, J. Amer. Chem. SOC., 1959,81, 3507. 10 Ausloos and Lias, J. Chem. Physics, 1963, 38,2207. 11 Ausloos, Lias and Gorden, J. Chem. Physics, 1963, 39, 3341. 12 Sieck and Johnsen, J. Physic. Chem., 1963, 67, 2281. 13 Hauser, J. Physic. Chem., 1964, 68, 1576. 14 Hummel, Disc. Faraday Soc., 1963, 36, 75. 15 Hummel and Hearne, Chem. and I d . , 1961, 1827. 16 Jamieson and Brown, Can. J. Chem., 1964,42, 1638. 17 Jennings and Cvetanovic, J. Chem. Physics, 1961, 35, 1233. Callear and Pereira, Trans. 18 Clyne and Thrush, Proc. Roy. SOC. A, 1963, 275, 559. Larkin and Thrush, Disc. F a r d y Farachy SOC., 1963,59,2774. SOC., 1964, 37, 112.R. W. HUMMEL 19 Weiss and Bernstein, Physic. Rev., 1955, 98, 1828. 20 Melton, J. Chem. Physics, 1960, 33, 647. 21 Wexler and Jesse, J . Ameu. Chem. Soc., 1962, 84, 3425. 22 Shahin and Lipsky, J. Chem. Physics, 1964, 41, 2021. 23 Frey, J. Amer. Chem. Soc., 1960, 52, 5947. 24 Duncan and Cvetanovic, J. Amer. Chem. Soc., 1962, 84, 3593. 25 Mantcn and Tickner, Can. J. Chem., 1960, 38, 858. 26 Mahan and Mandal, J. Chem. Physics, 1962, 37, 207. 27 Bell and Kistiakowsky, J. Amer. Chem. SOC., 1962, 84, 3417. 28 Magee, J. Chem. Physics, 1963, 39, 855. 29 Morrison, J . Chzm. Physics, 1953, 21, 1767. 30 Cermak and Herman, Nucleonics, 1961, 19, 106. 31 Field and Franklin, J. Amer. Chem. Soc., 1961, 83,4509. 32 Wilkinson and Johnston, J. Chem. Physics, 1950, 18, 190. 33 Mulliken, J. Chem. Physics, 1935, 3, 517. 34 Lassettre and Francis, J. Chem. Physics, 1964, 40, 1208. 35 Bowman and Miller, J. Chem. Physics, 1965, 42, 681. 69

ISSN:0014-7672    

DOI:10.1039/TF9666200059

出版商:RSC    

年代:1966

数据来源: RSC