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 bet ween Chemistry Physics and Biology Volume 63 1967 Pages 1-1568 THE FARADAY SOCIETY LONDON 0 The Faraday Society and Contributors 1967 PRINTED IN GREAT BRITAIN AT THE UNIVERSITY PRESS ABERDEEN

ISSN:0014-7672    

DOI:10.1039/TF96763FP001

出版商:RSC    

年代:1967

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 study of Sciences lying between Chemistry Physics and Biology Volume 63 1967 Pages 1569-3 I 36 THE FARADAY SOCIETY LONDON @ The Faraday Society and Contributors 1967 PRINTED IN GREAT BRITAIN AT THE UNIVERSITY PRESS ABERDEEN

ISSN:0014-7672    

DOI:10.1039/TF96763FP003

出版商:RSC    

年代:1967

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. Nuclear Magnetic Resonance Studies of Heterocyclic Fluorine Compounds Part 2.1-Perfluoro-N-Fluoro-Piperidine and Perfluoro-N-Fluoro-Morpholine Ring Systems BY J.LEE AND K. G. ORRELL * Department of Chemistry The University of Manchester Institute of Science and Technology Received 5th September 1966 The temperature-dependence of the 19F nuclear magnetic resonance spectra of perfiuoro-N-fluoro- piperidine and perfluoro-N-fluoro-morpholine has been examined in the range from -74 to 20°C. The changes in appearance of the spectra are interpreted on the basis of the changing rate of chair-to- chair interconversion. There is evidence that at corresponding temperatures this interconversion rate is greater for the perfluoro-N-fluoro-morpholine than for the pefluoro-N-fluoro-piperidine ring. The spectra of perfluoro-(N-fluoro-methylpiperidines) are essentially temperature-independent over the range from -90 to 100°C suggesting conformationally rigid structures.The effect of the per- fluoromethyl substituent on the vicinal ring fluorines is considered. The inversion of cyclohexane between its two chair conformations has been widely studied 2-5 by the nuclear magnetic resonance technique. From the low-temperature variation of the 1H spectrum of cyclohexane values of the entropy and the enthalpy of activation for the inversion process have been obtained. To date the study of inver- sion rates in piperidine morpholine and their N-alkyl derivatives has been less exten- sive.6-8 Furthermore there are some discrepancies between earlier 6 and later 7 9 8 results. For the perfluoro-analogues of the above compounds one might expect that replacement of all hydrogens by the bulkier fluorines would considerably reduce the rates of ring inversion at corresponding temperatures.Although in general a reduction is found experimentally it is not pronounced. The energy barrier is not a simple function of the size of the ring-attached atoms. Thus Tiers 9 found that the first-order rate constant for ring inversion in perfluorocyclohexane was almost identical with that measured for cyclohexane at - 66~5°C. He explained this result in terms of intrinsic torsional strain resulting from steric or electrostatic lY3-diaxial fluorine- fluorine repulsions an effect which is relieved in the activated complex. Reeves and Wells 10 have examined the temperature-dependence of the 40 Mc/sec 19F spectrum of perfluoro-N-fluoro-piperidine and by means of a spin-echo method have obtained a value of 6.1 f 1.5 kcal mole-1 for the energy barrier associated with the ring inversion process.The present paper compares this inversion rate with that observed in perfluoro- N-fluoro-morpholine and also investigates the effect on the motion of substituting a perfluoromethyl group for one of the fluorine atoms in the 2- 3- or 4-positions of the perfluoro-N-fluoro-piperidine ring. * present address Department of Chemistry The University of Exeter. 16 J . LEE AND K. G . ORRELL 17 EXPERIMENTAL Perfluoro-N-fluoro-piperidine,lll12 the three perfluoro-(N-fluoro-methylpiperidines)l~ and perfiuoro-N-fluoro-morpholine 14 were prepared by members of the fluorine research group of this department.High resolution 19F nuclear magnetic resonance spectra were recorded on an Associated Electrical Industries RS2 spectrometer operating at 60 Mc/sec and fitted with accessory variable temperature equipment .1 Perfluoro-N-fluoro-piperidine and perfluoro-N-fluoro-morpholine were examined in solutions containing 15-20 % v/v CFC13 this also serving as an internal reference. The three derivatives of perfiuoro-N-fluoro- piperidine were examined as neat liquids CF3C02H being used as an external reference. Chemical shifts measured relative to the latter reference were converted to the CFC13 reference scale by the addition of 76.5 p.p.m. [the mean separation between CF3C02H (ext.) and (15-20 %) CFC131. No corrections for bulk susceptibility differences or for temperature- dependence of reference absorption were applied and as a consequence it is estimated that all quoted chemical shifts are accurate to f 1.0 p.p.m.However differences of chemical shift from one sample to another are estimated to be accurate to - f o e 5 p.p.m. RESULTS PERFLUORO -N-F LU ORO -P IPER IDINE As the temperature-dependence of the 40 Mc/sec spectrum of this compound has been reported by Reeves and Wells,lO our results at 60 Mc/sec will be only briefly TABLE AS ASSIGNMENT OF INDIVIDUAL BANDS IN THE SPECTRA OF PERFLUORO-N-FLUORO- PIPERIDINE AND PERFLUORO-N-FLUORO-MORPHOLmE compound (temp.) I (- 74°C) F (I) band n0.O 1 2 3 5 6 8 10 12 7 9 11 13 4 1 2 3 4 5 6 position (clsec) 6256 6443) 6690 6873) 7172 7451) 7352 7632) 6808 4685 4846} 6624 6760 assignment 2a 6a 2e 6e 3a 5a 3e 5e 4a 4e NF 2a 6a 2e 6e {2 3 NF chem.shiftb centre (p.p.m.1 106.2 1 112.7 1 . 109.5 133.9 125.1 142.7 113.5 113.5 79'6 ] 86.4 93.2 110.4 110.4 112.7 112-7 centre at ambient temp. 109.2 131.3 133.6 113.0 86.2 110-3 112.4 a Numbers indicate the order of bands in increasing field direction ; there is also a correspondence b Relative to CFC13 ; positive values indicate that the reference absorbs at lower field. c Based upon the assumption that equatorial fluorines are generally more highly shielded than axial with fig. 2d. ones. 18 N.M.R. OF NITROGEN HETEROCYCLES summarised. Spectra were recorded in the temperature range from -74 to 2405°C. At ambient temperatures the spectrum consists of four broad structureless bands. This is compatible with the molecule rapidly interconverting between its two equiva- lent chair forms since this process effectively averages the chemical shifts of axial (a) and equatorial (e) fluorines in each of the CF2 groups.The assignment of bands in the ambient temperature spectrum and the change in appearance of the spectrum on lowering the sample temperature were in harmony with previous work.10 At the lowest temperature - 74"C the spectrum consisted of 13 absorption bands comprising three AB patterns 15 due to the 2- 3- and 4- CF2 groups and a single NF resonance. The general appearance clearly indicated that the ring inversion process was sufficiently retarded for the a- and e-fluorines of each CF2 group to be distinguished. The temperature-independence of the NF absorption indicated that even at - 74"C there was rapid inversion at the nitrogen.The assignment of each absorption band is presented in table 1 and is based upon the assumptions that (i) 2-fluorines because of their proximity to the electronegative nitrogen absorb at lower applied magnetic field than 3-fluorines and (ii) in any perfluoromethylene group the equatorial fluorine is more highly shielded than the axial fluorine. The latter assumption has been sub- stantiated for substituted perfluorocyclohexanes by Homer and Thomas,l6 but is directly opposite to an assumption of Reeves and Wells.10 PERFLUORO-(N-FLUORO-2-METHY LPIPERIDINE) The ambient temperature spectrum of this compound (presumably a racemic mixture) is shown in fig. 1. The observed pattern of bands can be analyzed as a 158.2 p.p.m. 72.8 FIG. 1 .-Ambient temperature spectrum of perfluoro-(N-fiuoro-2-methylpiperidine).series of overlapping AB sub-spectra due to the non-equivalent axial and equatorial fluorines of each CF2 group in the molecule. The observation is incompatible with a rapid interconversion between two equally abundant chair conformations (invomers) as in perfluoro-N-fluoro-piperidine and is indicative of an overwhelming abundance of one invomer (for each enantiomorph). The remaining bands in the spectrum are due to the CF3 the NF and the CF fluorines. The complete assignment of the spectral bands is given in table 2. Assignment to the various CF2 groups is based upon analogy with the unsubstituted molecule. On closer examination the perfluoro- methyl absorption was found to consist of eight components in the form of a doublet (1 J I = 20-2 c/sec) of doublets (1 J I = 14.4 c/sec) of doublets (1 J 1 = 10.9 c/sec).It is not possible to say with certainty to which fluorine nuclei the CF3 group is coupling but it i s likely to be those in the tertiary and 3-positions. This cannot be confirmed from the tertiary and AB systems since all their component bands are broad and do not exhibit any fully resolved fine structure. The spectrum was J. LEE AND K. G. ORRELL 19 TABLE 2.-kIGNMENT OF INDIVIDUAL BANDS IN THE SPECI'RA OF PERFLUORO-(N-FLUORO- METHYLPIPERIDINES) compound F2/ FKcF3 / \F2 31 I F band no.= 1 2 4 5 6 7 9 11 12 8 10 13 14 3 15 1 2 3 4 5 7 8 9 10 11 12 13 6 14 1 2 3 4 6 1 8 9 10 5 11 position tclsec) * 4368 6604 6798) 6153 9493 4208 6122 6285 6469) 7816 8115) 678 1 11041 4223 6355 6601 6784) 6882 7 167) 6745 11317 assignment C CF3 6a 6e 3a 3e 4a 5a 4e 5e NF 2-F CF3 2a 2e 6a 6e 4a 5a 4e 5e NF 3 -F CF3 2a 6a 2e 6e 3a 5a 3e 5e NF 4-F chem.shift b b.p.m.1 72.8 102.6 111-4 120.9 132.1 122.9 141-3 102.6 158.2 70.1 102.0 106.6 112.8 121.1 132.2 138.6 113.0 184.0 70-4 104.7 111.3 117.5 130.8 112.4 188.6 a Numbers indicate the order of bands in increasing field direction; there is also a correspondence b Relative to CFC13 ; positive values indicate that the reference absorbs at lower field. C Based upon the assumption that equatorial fluorines are generally more highly shielded than with fig. 1. axial ones. essentially unchanged in the temperature range from -90 to 130°C thus supporting the previous suggestion that this molecule is essentially conformationally rigid (nitro- gen inversion excepted). 20 N .M . R . OF NITROGEN HETEROCYCLES PERFLUORO-(N-FLUORO-3-METHYLPIPERIDINE) The analysis of the ambient temperature spectrum of this compound (or racemic mixture) was achieved by comparison with the spectrum of perfluoro-N-fluoro- piperidine and perlluoro-(N-fluoro-2-methylpiperidine). Again the spectrum was characteristic of a single inversion isomer. Three of the four perfiuoro-methylene groups produced separate AB patterns; the remaining CF2 (attributed to the 2- position on the ring) gave a single band due apparently to fortuitous chemical equiva- lence of its two fluorine atoms. The assignment of all the spectral bands is given in table 2. With the exception of the absorption due to perfluoromethyl all the bands were broad exhibiting complicated but not fully resolved fine structure.The CF3 resonance was a symmetrical 1 4 6 4 1 quintet (I J I = 13.8 c/sec) of doublets (1 J I = 6.6 c/sec) apparently resulting from near equal coupling to the four fluorines in the vicinal CF2 groups and a weaker coupling to the tertiary atom. This spectrum was essentially temperature-independent in the range from - 90 to 100°C. PERF LU O R 0 - ( N-F LUO RO - 4 -MET H Y L P I P ER 1 DINE) The ambient temperature spectrum of this compound followed the pattern expected from the previous two compounds. Thus the two types of non-equivalent CF2 groups in this molecule gave rise to AB patterns the individual components of which are assigned in table 2. As in the 3-substituted isomer the CF3 resonance was a quintet (I J I = 12.9 c/sec) of doublets (I J I = 6.2 c/sec) the interpretation of this being the same as previously.The spectrum was virtually independent of temperature in the range from -90 to 100°C. PERFLUORO-N-FLUORO-MORPHOLINE At ambient temperatures the spectrum consists of three absorption bands which are compatible with the molecule rapidly interconverting between its equivalent chair TABLE 3 .-TEMPERATURE-DENDENCE OF THE 60 MC/SW SPECTRUM OF PERFLUORO-N-FLUORO- MORPHOLINE temp. (“(3 28 7 - 20 - 30 - 38 - 47 - 54 - 62 - 68 - 73 -75 6746 6746 6747 6758 6777 6782 6767 6770 6789 6767 26 29 23 25 24 22 21 25 25 26 6616 661 8 6633 6626 6641 6646 6627 6633 6644 6626 9 9 11 10 11 11 16 24 35 34 6760 32 6624 36 -4 6 Av3 5172 17 5174 19 5175 25 5169 60 5173 87 5295 220 - - - - - 4690 58 4841 48 5513 5670 4685 4846 66 5519 60 5669 56 0 Chemical shift (c/sec to high field of CFCI3).b Band width at half-height (c/sec). J . LEE AND K. G. ORRELL 21 structures and rapidly inverting at the nitrogen (fig. 2a). The band at lowest applied field was assigned to CF2-O-CF2 ; the remaining absorption systems were attri- buted to CF2-N-CF2 and NF the latter absorbing at the highest field and dis- tinguished by its integrated intensity. The temperature-dependence of the spectrum FIG. 2.-Spectrum of perfluoro-N-fluoro-morpholine at (a) 28°C; (b) -30°C; (c) -55°C; and (d) -775°C. from -75 to 28°C is summarized in table 3. The assignment of bands at the two temperature extremes is presented in table 1. On cooling the sample below room temperature the CF2-0 absorption band initially noticeably broader than the CF2-N band broadened considerably (fig.2.b) until at ca. -50°C it was so broad as to be undetectable (fig. 2c). At -7O"C the absorption reappeared as a set of four bands forming a typical AB system. At this temperature the CF2-N absorption had broadened a little but was still a single band. At -75"C the lowest temperature reached in this case the AB sub-spectrum was sharper but the CF2-N resonance was still a rather broad single band (fig. 24. The difference in behaviours of the CF2-0 and CF2-N portions of the spectrum to temperature lowering is caused by a smaller axial-equatorial internal chemical shift for the latter group. This would infer that a 22 N.M.R. OF NITROGEN HETEROCYCLES further decrease of temperature should enable axial and equatorial atoms of the group to be distinguished. DISCUSSION The temperature-dependence of the spectra of perfluoro-N-fluoro-piperidine and perfluoro-N-fluoro-morpholine can be interpreted in terms of a correspondingly dependent rate of chair-to-chair interconversion.The purpose of the present work was not to obtain exact quantitative measures of activation energies and pre-exponen- tial factors for this type of process but to gain an overall impression of the kinetics involved. Rough estimates of inversion rates at coalescence temperatures can be made by applying the equation 17 k = z ( ~ v ) / J2 to the AB sub-spectra ; k is the first-order rate constant at coalescence and 6v is the geminal internal chemical shift. The assumptions involved in the use of this equation have been presented previously.4 With perfluoro-N-fluoro-piperidine the 3- and 4- fluorine bands each coalesce at ca.-40°C. The internal chemical shifts between axial and equatorial fluorines in these CF2 groups are both ca. 1000 c/sec. Hence at -4O"C the rate of ring inversion must be about 2 x 103 sec-1. From the coal- escence of the 2-fluorine pattern it similarly follows that at -45°C the interconversion rate must be about 5 x 102 sec-1. These values roughly indicate how the rate of inter- conversion is reduced on lowering the sample temperature although the results are too approximate to allow substitution in an Arrhenius type equation in order to obtain an activation energy for the process. By spin echo techniques Reeves and Wells 10 have obtained a value of 6.1 & 1.5 kcal mole-1 for a 33 mole % solution of the material in CFC13. They observed the same changes in the spectrum as have been described here but at lower temperatures.For example they found it necessary to cool the sample below - 100°C for the AB patterns to be clearly resolved. The difference may be attributed (i) to the use of a lower radiofrequency 40 Mc/sec in the previous study and (b) to an effect of the solvent (CFC13) on the energy barrier-Reeves and Wells used a more dilute solution than in the present work. On the basis of transition state theory,l the present data yields an approximate activation free energy AG* of 10 kcal mole-1 at - 40°C. There are two possible causes (co-operative or independent) of the distinct differ- ence in temperature-dependence of the CF2-N absorption between perfluoro-N- fluoro-morpholine and perfluoro-N-fluoro-piperidine.The first possibility is a much smaller geminal internal chemical shift for the group in the former compound. This however seems unlikely. The second possibility is a higher rate of ring inversion in the cyclic ether at corresponding temperatures. This is supported to some extent by the coalescence behaviour of the CF2-0 absorption. The temperature of coalescence is ca. - 50°C. In the slow exchange limit the internal chemical shift for the geminal fluorines of the group is 814 c/sec so that at - 50°C the rate of ring interconversion must be approximately 2 x 103 sec-1 suggesting a slightly lower barrier in perfluoro-N- fluoro-morpholine than in perfluoro-N-fluoro-piperidine. This is compatible with the statement by Banks and Burling 14 that the ether link creates greater " molecular flexibility ".However some caution must be exercised in the comparison of the two molecules because of possible solvent effects. The low-temperature spectra of these two compounds provide information regard- ing the internal chemical shifts between geminal (i.e. axial and equatorial) fluorines 6vac and corresponding coupling constant moduli I Jae I. These values are listed in 3. LEE AND K. G. ORRELL 23 table 4 together with similar data obtained from the ambient temperature spectra of the perfluoro-(N-fluoro-methylpiperidines). The geminal coupling constants are virtually independent of the presence and position of attachment of the CF3 group (tables 4,5). The value of I Jae I is smallest for perfluoromethylene groups adjacent to TABLE 4.-GEMINAL INTERNAL CHEMICAL SHIFTS AND COUPLING CONSTANT MODULI FOR PERFLUORO-N-FLUORO-PIPERIDINE AND PERFLUORO-N-FLUORO-MOIUJHOLINE COMPOUNDS &k/ ring 6V.e position b.p.m.1 compound 2 6 6-5 185 I 3 5 19-2 282 4 17.6 285 I1 3 5 ? ? 2 6 13-6 156 6 8.8 199 I11 3 11.2 293 4 5 18.4 289 2 ca.0 ? IV 6 6.2 198 4 11-1 289 5 17.6 284 V 2 6 6.6 196 3 5 13.3 286 * For keys to compound and ring position numbers see tables 1 and 2. b Axial/equatorial internal chemical shift. TABLE 5-1 JaC I VALUES FOR THE PERFLUORO-N-FLUORO-PIPERIDINE RING ring position range (c/sec) (clsec) 2 6 185-199 195 3 5 282-293 287 4 285-289 288 the heterocyclic nitrogen atom. This is presumably due to the depletion of electron density between the coupling nuclei 18 by the electronegative nitrogen. This might also contract the FCF angle by a reduction in bond electron correlation.As one might expect the effect is even greater in the morpholine where a ring oxygen is also present. Values of I Jae I for the 3- 4- and 5-positions in the ring of the piperidine compounds agree with corresponding values obtained by Homer and Thomas 16 for substituted perfluorocyclohexanes where geminal couplings lay in the magnitude range 280- 290 c/sec. In contrast to the geminal coupling constant moduli corresponding internal chemical shifts are very dependent upon the presence and location of a CF3 sub- stituent. In perfluoro-N-fluoro-piperidine Gvae for the 2-fluorines is c6nsiderably smaller than for the 3- and 4-fluorines. In the perfluoromethyl-substituted com- pounds this order still holds but the CF3 group deshields the vicinal fluorines in such A 24 N.M.R.OF NITROGEN HETEROCYCLES a way as to reduce 6v by ca. 6-8 p.p.m. from its value in perfluoro-N-fluoro-piperi- dine (table 6). Furthermore on the basis of the assumption (originating entirely from the previous results of Homer and Thomas 16 for substituted perfluorocyclohexanes) that in any CF2 group the equatorial fluorine is more highly shielded than the axial fluorine this table further indicates that the effect of substituting a CF3 group for a fluorine atom in either the 3- or 4-positions is to deshield the vicinal equatorial fluorine by ca. 10 p.p.m. and the corresponding axial fluorine by ca. 4 p.p.m. This is completely analogous to the situation in perfluorocyclohexane derivatives.16 For the 2-substituted compound the shifts are ca. 1 and 9 p.p.m.respectively. TABLE ~.-DMHIELDING OF WCINAL FLUORMES BY A PERFLUOROhfETHYL GROUP 4 An * A e - 4 compound a posihon b.p.m.1 b.p.m.1 b.p.m.1 III 3 1.2 9.3 8.1 IV 2 4-2 10.7 6.5 4 4-0 10.5 6.5 V 3 5 4.6 10.6 6 . 0 * For keys to compound and ring position numbering see table 2. b Defined as the change in the axial or equatorial chemical shift (according to suffix) on replacing a vicinal fluorine by a CF3 group. In the perfluoro-(N-fluoro-methylpiperidines) the CF3 substituent could in principle be either akially or equatorially placed but from steric considerations the latter is more likely ; molecular models support this view. The experimental observa- tion of single inversion isomers at ambient temperatures is compatible with a signifi- cant difference in stability in each pair ; a large energy difference between the inversion forms would necessarily lead to a large barrier to inversion from the more stable structure.That this is the form with equatorial substitution is supported by the nature of the multiplet structure of the CF3 absorption in the 3- and 4-substituted compounds being a quintet of doublets. This implies equal coupling to the four fluorine nuclei in the adjacent ring positions a situation which would seem more probable if the CF3 group were equatorially oriented and thus symmetrically disposed towards the CF2 fluorines. Again this is similar to the derivatives of perfluoro- cyclohexane.16 In pe~uoro-(N-fluoro-2-methylpiperidine) where there is only one CF2 group adjacent to the substituent the multiplet structure of the CF3 sub-spectrum indicates unequal coupling to the CF2 group fluorines.This observation is therefore suggestive of an unsymmetrical disposition of the CF3 group towards the fluorines of CF2. This could arise if the CF3 group were axially attached but this seems highly unlikely. A more feasible explanation lies in a departure from the perfect chair form in the region of the heterocyclic atom. The parent compound perfluoro-N-fluoro- piperidine may experience distortion of the FCF tetrahedral angle in the 2-position. That a similar distortion exists in regard to the CCF angle in the 2-position of perfluoro- (N-fluoro-2-methylpiperidine) may be further evidenced by (i) the different gemind CF3-F coupling constant (irrespective of assignment) and (ii) the different effect of CF3 upon the vicinal fluorine chemical shifts (table 6) for 2-substitution in comparison with 3- or 4substitution.An extension to the range of perfluoro-N-fluoro-piperidine compounds studied here would seem desirable to produce conclusions of a more general and definite nature. However the results of the present work are similar to the more extensive work on perfluoro-(methylcyclohexanes).l6 A A J . LEE AND K . G. ORRELL 25 The authors thank Dr. R. E. Banks for clarification of the organic nomenclature and Prof. R. N. Haszeldine Dr. R. E. Banks J. E. Burgess E. D. Burling and W. M. Cheng all of the University of Manchester for the provision of the compounds studied. 1 J. Lee and K. G. Orrell Trans. Faraday SOC. 1965,61,2342. 2 F. R. Jenson D. S. Noyce C. H. Sederholm and A. J. Berlin J. Amer. Chem. SOC. 1960 82 3 R.K. Harris and N. Sheppard Proc. Chem. SOC. 1961,418. 4 W. B. Monk and J. A. Dixon J. Amer. Chem. SOC. 1961,83,1671. 5 A. Allerhand F-M. Chen and H. S. Gutowsky J. Chem. Physics 1965,42,3040. 6 A. T. Bottini and J. D. Roberts J. Amer. Chem. SOC. 1958 SO 5203. 7 J. B. Lambed and R. G. Keske J. Amer. Chern. SOC. 1966,88,620. 8 R. K. Harris and R. A. Spragg Chem. Comm. 1966,314. 9 G. V. D. Tiers Proc. Chem. SOC. 1960,389. 10 L. W. Reeves and E. J. Wells Disc. Faraday SOC. 1962,34 177. 11 R. E. Banks A. E. Ginsberg and R. N. Haszeldine J. Chem. SOC. 1961 1740. 12 R. E. Banks W. M. Cheng and R. N. Haszeldine J. Chem. SOC. 1962,3407. 13 R. E. Banks J. E. Burgess and R. N. Haszeldine J. Chem. SOC. 1965,2720. 14 R. E. Banks and E. D. Burling J. Chem. SOC. 1965,6077. 15 P. L. Corio Chem. Rev. 1960,60,363. 16 J. Homer and L. F. Thomas Trans. Faradzy SOC. 1963 59,2431. 17 H. M. McConnell J. Chem. Physics 1958,244,430. 18 J. Dyer Proc. Chem. SOC. 1963 275. 1256; J. Amer. Chem. SOC. 1962,84,386.

ISSN:0014-7672    

DOI:10.1039/TF9676300016

出版商:RSC    

年代:1967

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. Electron Spin Resonance and Torsional Motion of the B Protons of the HOOC-CH,-C(0H)-COOH Radical* BY CARLO CORVAJA Institute of Physical Chemistry University of Padua Padua Italy Received 25th July 1966 The e.s.r. spectrum of the free radical HOOC-CH&(OH)COOH formed by y-ray irradiation of single crystals of ammonium malate monohydrate has been recorded at different temperatures. The change in the p proton coupling constants with the temperature is discussed in terms of a torsional motion about the C a - 0 single bond. The C13 splitting and the hydroxyl proton splitting are corre- lated to the conformation of the hydroxylic group which results to be about 20” out of the radical plane.The temperature dependence of the coupling constant is consistent with the presence of strong intermolecular forces which hinder the motion. They probably arise from hydrogen bonds in the solid state. The p proton hyperfine coupling constant in a free radical of the type RRCH- eR”R” (where R R R” R” may be hydrogen atoms as well as substituents such as COOH alkyl groups etc.) depends essentially on the orientation of the C-H bond with respect to the plane of the CT bonds of the trigonal carbon atom.1 This fact opens the way to the study of the conformation of the free radicals by means of the e.s.r. spectroscopy. The conformation does not depend only on the nature of the radical but also on the surroundings. In solution the conformation is only due to the action of intramolecular forces whereas in the solid state the interaction of the radical with the crystal lattice may freeze the radical in a particular situation.The study of the conformation of a free radical in the solid state completes the knowledge of the position of these centres in the crystal lattice. From the orientation of the hyperfine tensor of the a proton (if one is present) one knows the orientation of the Ca-H bond and of the p orbital in which the unpaired electron is localized relative to the crystal axis. Owing to the sp2 hybridization of the a carbon atom these two data are enough to find the directions of all the Q bonds in the radical plane. From the p proton coupling which is generally nearly isotropic one gets the direction of the p bond with respect to the radical plane.In such a way the position of many atoms is known. The p protons may undergo a torsional motion about the Ca-CS bond and since this motion generally takes place at a frequency much higher than the hyper- fine coupling frequencies what one observes is an averaged situation. If the molecular motion is of large amplitude the coupling constant changes markedly from the value which corresponds to the equilibrium position and this possibility should be taken into account because it can lead to erroneous conclusions. In order to obtain good results it is desirable to have the spectra of the radicals trapped in different crystal lattices and possibily taken at different temperatures. Although the free radicals trapped in the crystal lattices undergo some motion sometimes of large amplitude nevertheless as yet the experimental results are in- sufficient in number 2 to give a good knowledge of the forces acting on the free radicals * This work is sponsored by the Italian National Research Council Chemistry Committee Center for Theoretical Chemistry.26 C . CORVAJA 27 in the solid state which restrict the motion. This paper is concerned with the e.s.r. spectra of the radical HOOC-CH-k(OH)-COOH trapped in single crystals of ammonium malate monohydrate. EXPERIMENTAL The crystals of monoammonium malate monohydrate were grown from a water+ ethanol solution containing the D-L mixture of the acids in the presence of NH40H. They are mono- clinic,3 class 2/m and they present the forms (1 10) and (01 1 ) equally developed with(010) poor 1 y developed .The crystals were irradiated with y-rays from a C060 source at a dose of 1-5 Mrad and were oriented by means of a simple goniometer mounted on the microwave cavity. The spectra at 77°K were taken with the crystal immersed in liquid nitrogen contained in a Varian V-4546 quartz Dewar while the other temperatures were obtained by allowing a stream of cold or warm nitrogen to flow past the crystal. The spectra were recorded with a Varian V-4501 X-band spectrometer equipped with 100 kc/sec field modulation. The field calibra- tions were performed by comparison with the spectra of the NO(SO& radical whose three lines are assumed to be 13 Oe apart. RESULTS The room temperature e.s.r. spectrum of the radical formed by y-ray irradiation of a single crystal of ammonium malate monohydrate has been reported.4 It consists I 1 I I 130 100 200 300 400 T"K FIG. 1.-Coupling constants of the two p protons as function of the temperature (curves (a)). The values are given by the scale on the right. The ratio UH/B calculated with harmonic vibrator wave functions is given by the scale on the left. The full curves and the dotted ones are calculated with force constants of 20 and 3 kcal/mole respectively. They correspond to angles 80 = 5 and 55". The stars indicate the experimental points adjusted to B = 130 Mcfsec. of four absorption lines whose separations depend only slightly on the orientation of the crystal in the magnetic field. For some orientations each one of the four lines is further split into a doublet with a small splitting constant. From the analysis of 28 HOOC-CH2-C(OH)-COOH RA D I C A L the spectrum it was concluded that the paramagnetic species involved is the radical HOOC-CH~-~(OH)COOH.The four lines with nearly isotropic splitting should arise from two p protons and the small anisotropic splitting from a hydroxylic proton. The coupling constants of the p protons change with the temperature and I have taken some measurements at different temperatures. The results are shown in fig. 1. In addition to the hyperfine lines deriving from the two fl protons and from the hydroxylic proton some other weaker lines are observed. These should arise from the free radicals containing the C13 nucleus ( I = 3) occurring in the natural isotopic FIG. 2.-E.s.r. spectrum of the HOOC-CH&(OH)COOH radical. The field is parallel to b.The orthogonal system of axes used is a* bc where a* is an axis orthogonal to the crystallographic axes b and c. Between the arrows the nominal gain of the 100 kc/sec amplifier was reduced by a fraction of 100. mixture to the extent of 1.1 %. The intensity of the " satellites " lines is about 0.5 % of that of the main lines. A typical spectrum is shown in fig. 2. The C13 splitting is anisotropic but we were not able to measure the hyperfine splitting tensor since for some orientation of the crystal the " satellites " lines disappear in the wings of the main lines. Only the largest principal value of the C13 hyperfine coupling tensor has been measured. It occurs with the magnetic field having the following direction cosines with respect to the reference system of axis 0.098 0.966 0.238.The C13 splitting does not change with the temperature within the experimental errors down to 77°K. DISCUSSION c13 AND HYDROXYLIC PROTON For the HOOC-CH2-C(OH)COOH radical the absence of a protons does not allow to study the orientation of the radical in the crystal with respect to the crystal axes. For free radicals in which the unpaired electron is localized in a p z orbital centred on a C13 atom the C13 hyperfine coupling has its maximum value when the field H is directed along the z axis.5 The values measured in such directions range from 212 to 238 Mc/sec.5-7 We found a maximum value of 232 Mc/sec in the direction 0.089 0.966 0.238 which should correspond to the direction of the p z orbital in our radical. However an indication may be derived from the C13 splitting.C . CORVAJA 29 Unfortunately the crystal structure of ammonium malate monohydrate is unknown so that a comparison with the position of the undamaged molecules is not possible. The measurement of the hydroxylic proton hyperfine tensor taken by Rao and Anderson 4 requires some discussion. The principal values of the hyperfine tensor are 0 +3 & 17 Mc/sec. If we assume the positive sign the isotropic part is + 6.6 Mc/sec and the anisotropic parts are - 6.6 - 3.6 and + 10-4. They are in accord with those of glycolic acid radical in lithium glycollate even if lowered by a factor of 1/3. For this latter radical the largest value + 15 occurs with the magnetic field approxi- mately parallel to the 0-H bond. We suppose that also in the radical HOOC-CH2 -e(OH)COOH the direction of the largest principal value + 10.4 is that of the O-H bond.The small value of the isotropic part of the hydroxyl proton in the glycolic acid radical has been accounted for by the position of this proton almost in the plane of the radical.4 In such a situation the angle between the direction of the p z orbital and the direction of the 0-H bonds should be about 90". From our data on C13 splitting the result is 70". The isotropic coupling of the hydroxyl proton in the H-k(0H)COOH radical in lithium glycollate monohydrate whefe the proton is in the radical plane is -7 Mc/sec.s The value we found is of opposite sign and is an indication of a twist of the C-H bond with respect to the radical plane. According to Derbyshire,lo the iso- tropic coupling of a hydroxyl proton should derive from the two concurrent mechan- isms a polarization of the 0-H bonds caused by the spin density on thep orbital of the oxygen atom and a hyperconjugation with unpaired electron of the proton.The first mechanism is operative when the proton is in the radical plane and it gives rise to a negative spin density and coupling constant. The second one takes place when the proton is out of the plane and gives rise to positive spin density. Pooley and Whiffen have found a positive value for the radical H-e(0H)COOH trapped in anhydrous lithium glycollate 8 where the hydroxyl proton is 60" out of the radical plane. It has been suggested 9 that for a B proton linked to an oxygen atom the coupling constant is given by with BO = -9 Mc/sec and B = 87 Mc/sec. With these values of the constants we obtain in our case an angle of 65" which in a good agreement with the value obtained from the C13 splitting.UH = B + B cos2 8 (1) /3 PROTONS The p proton coupling constant is related to the angle 8 formed by the direction of the p z orbital and the projection of the Cb-H bond on the plane perpendicular to the CU-@ bond by the equation When the bond is not locked but undergoes some torsional motion about on equili- brium position eqn. (2) is still valid if we substitute cos2 8 with the appropriate average aH = B cos2 e. (2) C O S ~ 8 = (JI 1 C O S ~ 8 1 JI} or when more states are thermally accessible (3) 30 HOOC-CH2-C(OH)-COOH RADICAL $ represents the wave function which describes the motion and n is an index numbering the various states. When motion occurs cos2 8 and therefore the coupling constant a H should in principle depend on the temperature and this variation is governed by the wave functions and the eigenvalues of the torsional vibrator.Both these quantities are hard to obtain since they presume a knowledge of the form of the potential which hinders the motion and the possibility of solving the Schroedinger equation with this potential. However some qualitative informations may be obtained by the analysis of two limiting cases. If the motion takes place in a potential well which is a constant in a range of angles and very high outside the wave functions are such that the matrix elements are all equal and therefore a change in the population of the states does not affect the coupling constant. The case of a harmonic potential has been discussed by Griffith 11; the matrix elements of cos2 8 for the different states depend on n and therefore cos2 8 should change with the temperature.I have performed some calculations of the average cos2 8 at different temperatures using eqn. (8) of ref. (1 1) with I = 110 x 10-40 g cm2 and various values of Y in the range 3-20 kcal/mole. This range contains the values observed for the barriers to the internal motion in molecules of this type. It may happen that the potential is well described by a harmonic term near the bottom and rises very rapidly when the angular displacement becomes large. We may then think that the wave function would be very close to those of the harmonic oscillator for low energy and to those of a particle in a box when the energy of the system rises. In order to compare qualitatively the experimental data with the calculated ones we must know the value of B and 80 which appear in (8) of ref.(1 1). If the two protons in the HOOC-CH2-d(OH)COOH radical are locked at 77"K the two coupling constants are given by the simple relationships - at = B c0s2 8 a; = B COS' 02 in which the angles 81 and 82 are related one to the other by the fact that their sum must be either 60" or 120" 1 owing to the sp3 hybridization of the carbon atom. On substituting the experimental values * we obtain 8 = 5" 8 = 55O B = 110 Mclsec. Values of B in the range 1 10-140 Mclsec have been reported and a value of 1 10 even if of the correct order seems to be too low indicating that at 77°K some degree of motion is still present. We tentatively assume a value of 130 Mc/sec for the qualita- tive description of our system.The calculated values of cos2 8 have been used to predict the variation of the ratio aH/B as a function of the temperature for 80 = 5 and 55". The results are shown in fig. 1 where the experimental values of aH/B adjusted with B = 130 Mc/sec are also indicated. The model of an harmonic oscillator predicts a larger variation of the coupling constants with the temperature than that observed in our case. This fact suggests that the potential well which hinders the motion of the p protons in the radical HOOC-CH~-~(OH)COOH trapped in ammonium malate * The values we use are not strictly the isotropic part of the coupling constant but the values obtained mith the magnetic field parallel to the b axis. However the value measured in this direction at room temperature is close to the isotropic coupling and the small anisotropy does not affect our qualitative discussion.C. CORVAJA 31 monohydrate crystals should rise rapidly as the displacement from the equilibrium position becomes appreciable. Our knowledge of the forces which are involved may be only qualitative and in our treatment we must suppose that the torsional motion of the /? protons is not coupled with other motions in the radical. However it seems established that in our system the forces are comparably higher than those which hinder the motion of the /3 protons in the radicals so far studied.lO* 139 14 15 These forces may be intramolecular or intermolecular and probably arise from the presence of hydrogen bonds. The latter case is the most probable on the basis of the e.s.r.spectrum of the HOOC-CH2 -e(OH)COOH radical in aqueous solution. The radical has been produced by reaction of malic acid with OH radicals and the coupling constants of the /? protons in these conditions are both 28 Mc/sec.ls This small value may be accounted for by an equilibrium conformation in which the angle 8 of the /? protons is nearly 60" and the carboxylic group is above or below the radical plane. The conformation is then different in solution where only intra- molecular forces are involved. I am especially indebted to Prof. Giovanni Giacometti for his continuous interest in this research and to him and Dr. P. L. Nordio for enlightening discussions. I thank Dr. Cordischi and Prof. Busulini for the irradiation of the samples. 1 C. Heller and H. M.McConnelI J. Chem. Physics 1960,32 1535. 2 An account of these studies may be found in a paper by R. Mam in Molecular Relaxation Processes. (The Chemical Society London 1965). 3 Groth Clzemische Kristallogruphie (Wilhelm Engelmann Leipzig 1910) vol. 3. 4 M. J. Rao and R. S. Anderson J. Chem. Physics 1965 42 2899. 5 H. M. McConnell and R. W. Fessenden J. Chem. Physics 1959,31 1688. 6 T. Cole and C. Heller J. Chem. Physics 1961 34 1085. 7 R. J. Cook J. R. Rowlands and D. H. Whiffen Mol. Physics 1963,7 31. 8 D. Pooley and D. H. Whiffen Trans. Farday Soc. 1961,57 1445. 9 D. H. Whiffen Coll. Int. Centre National de la Recherche Scient$que Paris (June 1966). 10 W. Derbyshire Mol. Physics 1962,5,225. 11 0. H. Griffith J . Chem. Physics 1964 41 1093. 12 C. Corvaja J. Chem. Physics 1966 44 1958. 13 M. Kashiwagi and Y. Kurita J. Chem. Physics 1963 39 3165. 14 I. Miyagawa and K. Itoh J. Chem. Physics 1962 36 2157. 15 A. Horsfield J. R. Morton and D. H. Whiffen Mol. Physics 1962,5 115. 16 A. B. Dixon R. 0. C. Norman and A. B. Buley J. Chem. Soc. 1964,3625.

ISSN:0014-7672    

DOI:10.1039/TF9676300026

出版商:RSC    

年代:1967

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. Absorption Spectrum of Bromine from 6200 to 51002$ BY J. A. HORSLEY AND R. F. BARROW Physical Chemistry Laboratory Oxford University Received 26th September 1966 The absorption spectrum of the 3110+u-1&! system of bromine between 6200 and 5100A has been photographed at high resolution using each of the separated isotopic species 79Br2 and 81Br2.A rotational analysis of ten bands of each isotopic species has been carried out. The accepted vibra- tional numbering was confirmed. The constants obtained (cm-1) for each species are :- 79Br2 W = 325.37 W = 168.88 x&$ = 1.75 Y ~ O = -00061 &' = 0.082114 Bi = 00594 U = 0.00043 y = -0oooO1 X:O; = 1.098 I$ = 0*00032 r; = 22809 r = 2-68 A. up" = 321.29 0 = 16683 ~ b i = 1.71 Y ~ O ; = -0W57 X ~ O ; = 1.064 &' = 0-080088 a," = 0000319 Bi = 00576 a; = 000038 y; = -o*m11 r; = 2.2809 ri = 2-69A. Revised constants for the most abundant isotopic species 79 81Br2 have been calculated. The last four bands immediately preceding the onset of the continuum have also been analyzed for each species. A limiting curve of dissociation has been plotted in each case leading to an average value for DO (79 81Br2) of 15,893.1 f 1.0 cm-1.The absorption spectra of the 3rIof-1Z+ systems of both C12 and 12 have been re-analyzed recently.1-3 In both cases the accepted vibrational numbering for the upper state was found to be in error and the constants for the upper state and ground state were revised. An analysis of some of the bands of the corresponding system of Br2 carried out by us in order to obtain an accurate potential curve by the Rydberg- Klein-Rees method indicated that the accepted constants for this molecule might also require revision. The absorption spectrum of the main system of bromine was first photographed at high resolution by Brown,4 who analyzed 13 bands of the most abundant species 79 81Br2 and obtained rotational and vibrational constants for this species.He also analyzed a number of bands of the less abundant isotopic species 79Br2 and 81Br2 and confirmed his assignment of the vibrational numbering of the upper state obtained from an earlier vibrational analysis. No further work on the rotational structure of the bromine bands has been published. Between 6,000 A and the onset of the continuum at 5108 A the spectrum shows little structure and the density of lines is great. This arises partly because natural bromine consists of a mixture of three isotopic species 79Br2 81B1-2 and 79 81Br2 with relative abund- ancies close to 1 1 2 respectively. In order to simplify the spectrum and reduce the blending caused by the high density of lines the separated isotopic species 79Br2 and 81Br2 were used instead of the natural mixture.32 The absorption spectrum of natural bromine is extremely complex. 1 I i - 1 E 0 P- 10 2 - I E 0 c I- 9 I. n 0 co 5 Y To face page 33.1 J . A. HORSLEY AND R. F. BARROW 33 EXPERIMENTAL The samples of 79Br2 and *1Br2 were prepared from isotopically pure K79Br and K8lBr. Very small amounts of bromine could not be prepared by the usual wet method oxidation of KBr with concentrated sulphuric acid as the bromine evolved was absorbed by the small quantity of acid distilled over with it. Oxidation of KBr with solid chromium trioxide was a suitable dry method of preparation. Adequate yields of bromine were obtained with no unwanted by-products. The apparatus used is shown in fig. 1. The part of the apparatus used for the preparation was sealed on to an absorption cell consisting of a Pyrex tube 1 m long and 3 cm diam.with Pyrex windows sealed on to each end. A short side-arm was joined on to each end of the cell. The apparatus used for the preparation consisted of two Pyrex tubes approximately 10 cm long and closed at one end connected by a short length of narrow tubing. The top of one of these tubes was sealed on to a side arm of the absorption cell. FIG. 1.-The absorption cell and apparatus for the preparation of isotopically pure Brz. About 20 mg of the isotopically pure KBr was placed in the open tube and about 0.1 g of dry CrO3 placed on top of it. The lower part of the other tube was cooled in liquid air. The reaction tube was stoppered and the mixture heated gently. Bromine vapour was evolved immediately and was distilled into the cooled collecting tube.When the reaction was complete the whole apparatus was evacuated. The reaction tube was sealed off and removed and %ally the whole apparatus was sealed off under vacuum. Bromine was then allowed to e orate into the absorption cell. The weight of KBr used in the preparation was sufficient bo obtain a pressure of about 2 mm Br2 in the absorption cell. The absorption spectrum was photographed over the range 62WA to the onset of the continuum at 5108 A using a 3.4 m Jarrell-Ash Ebert spectrograph which had a reciprocal dispersion of about 0-5A/mm and a resolving power of up to about 500,000 in this region. A high-pressure xenon arc was the source of continuous illumination and exposure times varied from 2 to 5 min. The plates used were high contrast Ilford R52 plates.The lines of an iron hollow cathode lamp were used to provide standard wavelengths. The lines of the spectrum were measured on a Zeiss AbbB comparator capable of reading to 0.0001 cm. The accuracy of measurement was estimated at &0.02 cm-1. Plate 1 shows part of the 12-2 band of 81Br2 and the onset of the continuum at the dis- sociation limit of 8lBr2. ANALYSIS AND CALCULATION OF CONSTANTS The transition has been established 5 as 3 1 1 g + u - 1Zl and hence the bands consist of P and R branches only. The bands show an intensity alternation the lines with odd J being stronger than those with even J. Compared with the spectrum of natural bromine considerably more structure was visible and the analysis was straightforward. Approximately 800 lines of the spectrum of each molecule were assigned to 10 different bands.In order to confirm that the lines had been assigned correctly and to check the rotational numbering of each band a preliminary set of constants were obtained by fitting the lines of each band to the expression v = vo + 2Bm -+ ABm(m f I)+ 4Dm3 - ADm2(m + 1)’ where rn = J+ 1 for an R line = -J for a P line. 2 34 ABSORPTION SPECTRUM OF BROMINE B and D are the lower state values for these constants AB and AD are the differences between the lower and upper state values of these constants. Final values of the constants were obtained using a method devised by Aslund 6 in which the term values of the upper and lower states of all the observed lines are calculated relative to a pair of arbitrarily chosen reference levels. The rotational constants for each vibrational state were then obtained from the term values by poly- nomial fitting.This method leads to constants of greater accuracy than those ob- tained by conventional methods. The values of Bv and Dv obtained in this way are given in table 1. TABLE 1 .-ROTATIONAL CONSTANTS cm-1 XIS,+ = 0 1 2 3 3rI()+" = 9 10 11 12 13 16 17 19 8.1948 &0*0010 8.7643 f0.0007 8.1308 f04007 8.0988 f0.0007 5.4341 f0.0010 5.3687 f0.0008 5-3039 f0.0008 5.2363 f0.0007 5- 1 644 & 0.0007 4.9399 f0.0008 4.6988 f0.0008 lWD 1.8 f0-35 2.6 f0-25 1.9 50.2 2.1 f0-2 4.8 f0.4 4.4 f0.2 5.0 10.2 5.2 f0.2 5.1 f0.2 5.5 5 0 . 3 7.4 f0.2 81Br2 1 OZB 7-9904 f0.0010 7.9640 f0.0007 7.9304. f0.0007 7.8954 fO.0010 5.3020 f0.0010 5.1773 10.0010 5-1 143 f0.0008 50482 f0.0006 4.8333 50-0009 4.7620 f0.0010 4,6005 50-0008 lO8D 2.0 f0-4 4.0 f0.2 2.4 f0.2 1.0 f0.5 3.2 f0.5 3.7 50.4 4.6 f0-3 5.4 f0.2 5.6 f0.3 7.0 f 0.4 7.2 f0.3 Limits are in all cases standard deviations.The relative rotationless term values for all the vibrational levels analyzed were also obtained by this method. The rotationless term values of the four vibrational levels of the ground state gave three values of the vibrational interval AG,++ These were fitted to the linear relationship The rotationless term values of the seven upper state vibrational levels were fitted to the expression G = constant+w,(v+~)-x,w,(v+~)2 AG,+ = o,-~x,co,(v+$). The accepted vibrational numbering was assumed to be correct. Using the vibrational constants for 79Br2 the isotopic shift in the band origin was calculated for each band analyzed.The calculated values of the shift together with the observed values are given in table 2. The agreement confirms the accepted vibrational number- ing. The vibrational constants obtained for each species are given in table 3 to- gether with the calculated values of the vibrational constants for 79 81Br2. The previously accepted vibrational constants are also given in brackets after the new values. The lower state B values were fitted to the linear expression B = B,-u(v++) J . A . HORSLEY AND R. F. BARROW 35 and the upper state B values to the expression The rotational constants obtained are given in table 4. B = B,-a(u++)+y(v+*)2 band 9-3 11-3 11-2 12-2 13-2 13-1 16-2 19-1 19-0 TABLE 2 band origin (cm-1) 79-79 16,2 1 3.68 16,473.95 16,792.73 16,917-01 17,037.37 17,358.34 1 7,3 74-23 17,995.19 18,318.36 81-81 16,211-68 16,469.69 16,784.61 16,9OTW 17,027-39 17,344.41 17,362-28 17,978.35 18,297.5 1 obs.shift (cm-1) 240 4.26 8.12 9.1 1 9.98 13.93 11.95 16.84 20.85 TABLE 3.vIBRATIONAL CONSTANTS OF BROMINE 79-79 81-81 lower state calc. shift (cm-1) 2.02 4.26 8.13 9.09 9.96 13-90 11-91 16.82 20.80 79-8 1 m 325.366 f0.003 cm-1 321.29 f0-02 cni-1 323.33 cm-1 (323.2) x:COL( 1.0985 f0.0003 1.064 f0-005 1.081 (1.07) upper st ate 0 168.88 10-1 cm-1 166.83 f0.1 cm-1 167.85 cm-1 (1 69.7 1) x;w; 1.75 zto.01 1-71 10.01 1.73 (1.91) Y;wL - 0.0061 f0.0002 - 0.0057 f0.0002 + 0.0059 (- ) Previously accepted values are given in parentheses. TABLE 4.-ROTATIONAL CONSTANTS OF BROMINE 79-79 81-81 79-8 1 lower state Be 0-0821 14 f0.000006 0.080088 f0-00002 0.081 101 (0.08091) re 2.2809 f0.0003 A 2.2809 f0.0003 8 2.2809 8 (2.28 A) a 0*000322 f0.000002 O.oO03 19 f0.000009 0.000321 (0.00028) D (Kratzer) 2-09 x 10-8 1.99 x 10-8 2-05 x 10-8 upper state Be 0.0594 f0-0002 0.0576 10.0002 0.0585 (0.0596) re 2-682 f0.005 A 2.690 f0.005 8 2-686 8 (2.65 A) a 0.00043 &O.ooOOl 0.00038 f0.00002 0-00041 (0.00062) Y - 0.0000 1 & 0~00OOOO4 - 0.0000 1 fO~OOOooo4 - 0.00001 (- ) D (Kratzer) 2.93 x 10-8 2.74 x 10-8 2.8 x 10-8 Previously accepted values are given in parentheses.DISSOCIATION ENERGY The region of the spectrum immediately before the onset of the continuum was examined in detail in order to obtain information about the rotational predissociation. Although the structure appeared to be very complicated it was possible to analyse the 36 ABSORPTION SPECTRUM OF BROMINE last four bands of each species (49-0 to 52-0).Determining the last line in the band proved difficult in some cases because there are so many lines in this region. How- ever it was possible to check the estimated last line by plotting the limiting curves of dissociation for the two isotopic species. The two curves obtained are almost identical which strongly suggests that the estimated last lines are correct. The two limiting curves are shown in fig. 2. The shape of the curves indicates that there is no I I I 5 0 0 1000 I S 0 0 2doo ’ JV+Q 19575 X last observed line; 0 first missing line. FIG. 2.-Limiting curves of dissociation for 79Br2 and *1Br2. maximum in the potential curve of the upper state. The two curves were extrapolated to give the term value of the convergence limit of the upper state relative to v” = 0 for each species.The two values are 79B1-2 = 19,577.2&0*5 cm-1; f31Br2 = 19,578.9 5 0 . 5 cm-1. The convergence limit corresponds to dissociation into a bromine atom in its ground state (2Ps) and a bromine atom in a 2P+ excited state. The 2P+ state lies 3,685 cm-1 above the ground state. Hence the dissociation energies D of the ground TABLE 5.-79Br2 bands immediately before the dissociation limit band vo(cm-1) B, 49-0 19,563.65 -0129 35 50-0 19,568-20 -01 14 28 51-0 19,571.77 -0097 23 52-0 19,574.47 ~0084 17 S of last line TABLE 6.-81Br2 BANDS IMMEDIATELY BEFORE THE DISSOCIATION LIMIT 49-0 19,562.28 -01 35 - 50-0 19,567-45 -0121 39 51-0 19,571.61 -0097 29 52-0 19,574.81 -009 1 20 band VO(Cm-9 B J of last line state of each species are 79B1-2 = 16,054.6 & 0.5 cm-1; f31Br2 = 16,054.3 f 0.5 cm-1.The value of DO for 79 -81Br2 is 15,893-1 cm-1 the error is not likely to exceed & 1 cm-1. For a predissociation observed in absorption the lines with upper levels above the true predissociation energy may not vanish completely but only become diffuse, J . A . HORSLEY AND R . F. BARROW 37 depending on the ratio of the transition probability to the decomposition probability. The above predissociation was observed in absorption only. So the true predissocia- tion may take place at a value of J lower than that observed as a slight broadening of the lines would not have been detected and therefore the above value may represent an upper limit for the dissociation energy of bromine. Previous measurements of the TABLE 7.-79Brz BANDS IMMEDIATELY BEFORE THE D~SSOCIATION LIMIT Wavenumbers of observed lines cm-1 49-0 50-0 51-0 52-0 J R(J) P(J) RQ P(J) R(J) P(J) R(J) P(J) 3 4 5 19,561-72 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 560.89 559.97 558.89 557.66 556.30 554.80 553.17 551.37 549.44 547.37 545-23 542-82 540.33 537.71 534.93 532.02 528-94 525.73 522.38 5 18-90 5 1 5-25 51 1-44 507.53 503-43 499.20 490.32 485.63 480.85 - 19561 -45 560.60 559.60 558.47 557- 1 8 555.79 554-22 55253 550.70 548.70 546.61 54-36 541.97 539.41 536.75 533.94 530.96 527.86 524.64 52 1 *24 517.71 514.04 510.21 506.23 502- 1 3 497.92 488.95 484-22 479.34 474.3 6 469.18 - 19,566.90 566.22 19,565.97 565-39 564.42 563-31 562-04 560.60 559.13 557-45 555.62 553.67 551.55 549.22 546-89 544.36 541.65 538.83 535.82 53271 529-39 526.02 522.38 5 18-73 514-78 565.10 564.08 562.92 561-64 560.20 558-63 556.89 555.03 553.03 550.88 548.57 546- 1 3 543.56 540.85 537.93 534.93 53 1.78 528.43 525.01 521.39 517.64 513.72 509.70 505.52 19,570-99 19,570-85 19,573.66 19,573-52 570.45 569-73 568-88 567.88 566.73 565.47 564.08 562.48 560.75 558.89 556.89 554.73 552.44 549.97 547.37 544.62 541.74 538.70 535.48 570.24 56950 568.61 567.61 566.42 565.10 563.65 562.04 560.28 558.38 556.30 554.15 551.80 549-32 546.7 1 543.91 541 *oO 537.93 534.68 527.76 - 573.08 572-36 570-45 569.34 568.02 566.56 564.95 563-20 561.31 559.27 557.06 554.73 - - 572.17 570.24 569-06 567.71 566.22 564.58 562.74 560.89 556.53 554.22 55 1 -62 548.97 - I position of the convergence limit of 79 81Br2 gave a value of 15,890 cm-1 for the dissociation energy,7 in good agreement with the above value.The information used to construct the limiting curves is summarized in table 5 for '9B1-2 and table 6 for 81Br2. The wavenumbers of the lines assigned to the last four bands of each species are given in tables 7 and 8. Enriched samples of 79Br and 8lBr were supplied by the Atomic Energy Research Establishment Harwell. 38 ABSORPTION SPECTRUM OF BROMINE TABLE 8.-SlBr2 BANDS IMMEDIATELY BEFORE THE DISSOCIATION LIMIT Wavenumbers of observed lines em-1 49-0 50-0 5 1 4 52-0 J R(J) P(J) N J ) P(J) R(Jl P(J) R(Jl P(J) 3 19,570-86 19,570.71 4 5 19,560-44 19,560.17 19,565.55 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 559.65 558.75 557.73 556.55 555.22 553.79 55220 550.48 548-61 546.63 54-51 542-26 539-86 537.35 534.66 53 1 *80 528.90 525.8 1 522.61 51 9-22 51 5-76 5 12.09 508.20 504-24 500.06 559.33 558.38 557.27 556.05 554.72 553.1 7 551.56 549.78 547.88 545.82 543.64 541.37 538.92 536.33 533.61 530.76 527.77 524.65 521.38 51 7.98 514.44 5 1 0.76 506.96 502.98 498.85 564-78 1 9.564.46 563.84 562.78 561.60 - 558-75 557.13 555.35 553.48 551 -45 549.27 546.96 544.51 54 1 -92 539.17 536-33 533.29 530.1 8 526-88 523-43 51 9.87 516.13 51 2.28 508.25 504.12 499-80 495-3 1 490.74 485.95 48 1 -08 476.03 470-79 465.47 563.50 562-37 561.12 - 558.21 556.55 554.72 552.76 550.74 548.52 546.1 5 543.64 541 -05 538.28 535.32 532.32 529- 1 1 525.8 1 522.35 518.73 5 14-94 51 1.07 507.05 502.84 498.52 494.03 489.42 484.59 479.67 474.61 469.42 458.52 452.88 - 570.30 569.59 568-84 567.86 566.76 565.55 564.16 562.66 559.22 557.27 555.22 552.99 550-63 548.1 1 545.49 542.72 539.76 536.66 533.45 530.1 8 526.80 523.28 515.51 - - 570.14 56940 568.58 567.51 566.42 565-14 563.70 562.1 7 560.44 558.65 556.68 554.54 552.34 549.92 547.38 544.70 541.92 538.92 535.81 532.52 529.1 1 525.64 522.03 51 8.21 514.15 19,572078 570.97 569.86 568.58 567.16 565.66 563.94 562.1 7 560.1 7 558.03 555.78 553-38 550.97 548-1 1 - 19,572.60 570-71 569-59 568.25 56676 565.25 563.50 561.60 559.65 557.49 555.22 552.76 - 1 A.E. Douglas C. K. Mdler and B. P. Stoicheff Can. J. Physics 1963 41 1174. 2 W. G. Richards and R. F. Barrow Proc. Chem. Soc. 1962,297. 3 J. I. Steinfeld R. N. Zare L. Jones M. Lesk and W. Klemperer J. Chem. Physics 1965,42,25. 4 W. G. Brown Physic. Rev. 1932,39,777. 5 R. S. Mulliken Physic. Rev. 1930,36,364. 6 N. Aslund Arkiv Fysik 1966,30 377. 7 A. G. Gaydon Dissociation Energies (Chapman & Hall London 1953) p. 66.

ISSN:0014-7672    

DOI:10.1039/TF9676300032

出版商:RSC    

年代:1967

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. Rotational Analysis of Bands of the Gaseous Au2 Molecule BY L. L. AMES AND R. F. BARROW Physical Chemistry Laboratory Oxford University Received 12th August 1966 The rotational analysis of the 2-0 and 3-0 bands of the A-Xsystem and of the 0-0 band of the B-X system has been carried out from plates of the absorption spectrum of gold vapour at about 2000°C. The bands of both systems consist of simple R and P branches and both transitions are considered to be 0; -12;. The internuclear distance r in the ground state is 2472 A.The existence of gaseous Auz molecules in gold vapour at elevated temperatures was first observed spectroscopically 1' 2 and the identity later confirmed by mass- spectrometric studies.3-5 The dissociation energy was found 5 to be 51.5k2.2 kcal. The vibrational analyses of the two observed band systems A-X (4800-6500 A) and B-X (3800-41OOA) have already been given (A-X;1' 6 B-X6). In the present paper the rotational analysis of three bands of these systems is described. EXPERIMENTAL Both the A-X and B-X systems of Au2 were studied in absorption in a King furnace at temperatures of about 2000°C and 20cm Hg pressure of argon. The bands were photo- graphed on a 3.4-m Jarrell-Ash plane grating spectrograph. The grating has 57,000 lines and is blazed for 59".Plates of the A-X system were taken in the 11 th order using Ilford R-52 plates while those of the B-X system were taken in the 15th order using Ilford N-50 plates. The reciprocal plate dispersion was 0.52 I$/m for the A-X bands and 0.33 I$/m for B-X. A high-pressure xenon arc served as the light source. The lines were measured on a Zeiss Abbe comparator against Fe hollow cathode standard lines whose wavelengths were taken from Lofthus's tables.7 ANALYSIS The bands analyzed were the 2-0 and 3 - 0 bands of the A-X system and the 0-0 band of the B-X system. The bands consist of only two branches each so that the transitions are 1Z+-JZ+ (or 0 + 4 + in case c). The branches can be expressed by the equation where m = J"+ 1 for an R branch and m = - J" for a P branch. The constants derived by least-squares solutions of the above equation for the three bands are given in table 1.v = vo + 2B"m + ABm(m + 1) - 4DNm3 - ADm2(m + 1)2 (1) TABLE CON CONSTANTS FOR BRANCH EQUATION cm-1 B-X o-O A-X 2 4 A-X 3 4 VO 25679.870 f0.025 19926.118 f0.013 20065.626 f0.018 B"x 102 2.79865 f0-0007 2.79663 f0-00083 2.79737 f0-00110 D"X 109 2.520 f0.048 2.386 50.153 2.458 f0.098 ABx 102 0-102525 f0.000009 0.2241 1 f0*00002 0.23236 rt0*00035 ADX 109 0.0836 f0-00085 1 123 f0-003 1 -209 f 0.002 39 40 GASEOUS AU2 MOLECULE The extent to which these equations fit the measured lines is illustrated in table 2 where values of the r.m.s. errors taken over groups of twenty lines are given. There is no systematic trend although it will be seen that the fit to the lines of the 2-0 band of the A-X system is somewhat better than for the 0-0 band of the B-X system.This is to be expected from the larger value of AB in the former band. TABLE VALUES OF THE r.m.s. ERRORS ( ( v o ~ - v ~ J 2 ~ n ) * IN UNITS OF 0.01 cm-1 FOR GROUPS OF 20 LINES 3-x A-X J 0-0 2-0 3-0 R P R P R P 61 -80 81-100 101-120 121 -140 141 -1 60 161 -1 80 181-200 201 -220 221 -240 241-260 261 -280 281-300 301 -320 321 -340 341-360 361-380 381-400 2- 6 2.1 1.3 0.8 1.3 2.8 2.7 2.3 2.0 1 *4 2.0 3.5 2.6 3.1 3.0 4.5 2.4 - 1.4 0.7 1.4 0.8 0.9 1.5 0.9 0.9 1.0 1.3 1.1 1.7 1.0 1.0 2.5 0.8 1.0 1.5 - 2-2 2.5 1.0 1.8 1.7 2.3 1.7 3.0 2.1 2.2 2.9 2.3 2.9 1-9 4.3 - 4.2 1.7 0.8 1.1 1.8 1.4 1.5 2-1 2.4 2.1 1-2 2.4 1.7 2.7 1.3 1.6 1.6 For heavy molecules such as A u ~ the rotational constants are so small that it is difficult to determine the correct numbering of the branches.An approximate numbering was however obtained by employing a rough estimate of the ground state B value the value of AB determined from the second difference between lines of a branch and the known vibrational frequency in the Kratzer relationship. The several possible numberings were reduced by the fact that 197Au has nuclear spin of 3/2. Assuming then that the nucleus obeys Fermi-Dirac statistics the relative statistical weights of the odd and even rotational levels of the ground state are as 5 3. Thus in absorption from the ground state 1Ei the lines of both the R and P branches with odd J values will be relatively stronger than those with even J values. The resulting strong-weak alternation of intensities in the lines of a branch is shown by the section of the B-X 0-0 band reproduced in fig.1. This ortho-para effect reduces the pos- sible number of both the relative and absolute numberings by a factor of two since a strong P line must correspond to a strong R line and all strong lines must have odd J values. With this limitation on the number of possible numberings it was now possible to select the correct relative numbering by matching the ground state combination differences obtained from the three bands. Some of the A2F" values are given in table 3. The absolute numbering was determined unequivocally from the several possible ones by a least-squares fit of both branches of a band to eqn. (1) with a computer. The numbering of the branches was altered independently so that both the relative and absolute numbering could be determined at once.The programme calculated PI40 176P 228R 25637-93 cni 1 FIG. I.-Part of the 0-0 band of the B-Xsystem of Au:. showing the alternation of intensities in the branches. [To fuce page 40. L. L. AMES AND R . F. BARROW 41 the values of the constants and their standard error for each fif as well as the value of w calculated from Kratzer's relation. The numberings which gave the lowest standard errors for the A-X 2 - 4 and 3-0 bands also had the same relative numbering as determined from the combination differences method. In addition the values of W" calculated for these numberings from the Kratzer relation were 191.5 and 188.8 which agree closely with the value TABLE 3.-Som VALUES OF THE GROUND STATE DIFFERENCES A#"(J) cm-1 J B-X o-O A-X 3 4 A-x 2-0 100 110 1 20 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 1 1 -26 12.33 13.45 14.56 15.65 16-81 17-91 18-99 20.07 21.20 22.29 23-37 24.45 25-57 26-64 27.72 28-87 29.88 30-93 32-07 33.03 34.12 35.23 22-26 23.39 24-49 25-53 26-64 27.7 1 28.79 29.88 30.94 32.04 33.08 34-14 35.20 11.25 12.35 13.46 14.53 15.65 16-76 17.88 18-97 20.09 21.13 22.25 23.39 24.46 25.57 TABLE 4.-GROUND STATE CONSTANTS OBTAINED FROM COMPUTER FIT OF LINES TO BRANCH EQUATION cm-1 band B ' x 102 Kratzer a" D" x 109 A-X 2 4 2.7966 f0.0008 191.5 2.39 f0.15 2.46 f 0.10 A-X 3 4 2.7973 f0*0011 188.8 fit 1 2.7986 f0.0007 186.6 2.52 &-0*05 fit 2 2-6782 f0-0007 186.9 2.20 f0-05 B-X 0 - 4 found by vibrational analysis of 190.7 cm-1.For the B-X 0 4 band two number- ings produced nearly equal minimum values for the standard errors and similar values for w".However as shown in table 4 only one of these two arrangements led to values of B" and of D" in agreement with those obtained from the A-X2-0 and 3 4 bands. As additional proof this arrangement is also the one giving equality of the ground state combination differences. Values of the molecular constants for A u ~ are given in tables 5 and 6. The values of YO Bv and Dv were obtained directly from the computer fit of lines to the branch equation. 42 GASEOUS A u ~ MOLECULE The values of B;J and 0; given in table 5 are the weighted means of those obtained from the three bands analyzed. The AG and a values for states X and A were deter- mined using the equation (written here for the state X) Ri(J)o - 0 - Ri(J)o - 1 = AGi - aJ(J + 1).(2) TABLE 5.-sPECrROSCOPIC CONSTANTS state I) YO Bv X 102 D" x 109 B 0 25679.870 f0-025 2.6961 f0.0007 2-604 f0.049 A 3 20065.626 f0.018 2.5650 f0.0012 3.667 f0.100 2 19926-118 f0.013 2.5725 f0.0009 3.509 f 0.1 60 XE+ 0 0 2.7977 f0-0005 2.499 f0.063 TABLE 6.-MOLECULAR CONSTANTS state dG UX 105 Be X 102 re(& B 9.63 (Pekeris) 2.7009 2.5 174 2.5958 2.5678 A (2-3) 139.682 f0.035 9-03 k0.05 X (0-1) 190.176 f0.014 7-23 f0.04 2.8013 2-47 19 p = 98.515 a.m.u. About 65 lines in the 0-1 band of B-Xwere numbered and used with the correspond- ing lines of the 0 - 0 band to calculate the constants for state X while lines of the A-X 2-0 and 3-0 bands were used for state A . The value of a for state B was calculated by the Pekeris relationship.These values of a were used to calculate Be and thus re for the three states. DISCUSSION ELECTRONIC STATES The mass spectrometric value DO of the dissociation energy is 5 51.5k2-2 kcal mole-1 or l8OlO+ 770 cm-1. Extrapolation of the ground-state vibrational levels gives 21060 cm-1. Considering the length of this extrapolation the agreement is satisfactory and confirms that state X is the ground state of A u ~ . The ground state of the Au atom is . . . 5dlo6s 2s and a pair of these ground state atoms give two molecular states 1Z and 3Cz. The 1C state is no doubt the ground state of Au~. Since the A B-X systems appear in absorption with short optical paths and since the bands of both systems possess only two branches R and P states A and B are identified as 1Zz or 0 in Hund's case c.The extrapolated value of the dissocia- tion energy of state A is 923Ocm-1 corresponding to a dissociation limit at 28880 cm-1 above v" = 0. This is close to the limit corresponding to Au W+Au 2DS/2 at 27170 cm-1 and state A may then reasonably be identified with the single 0 state arising from Au 2S+Au 2&/2. The vibrational analysis of the B-X system 6 shows the presence of bands with 0' as high as 12 at 27738 cm-1 above vA = 0 already above the limit corresponding to Au 2S+Au 2Dsp. State B must therefore arise from more highly excited atoms. The next highest pair is 20512+20512 at 36330 cm-1 but this pair gives no 0,' molecu- lar states. Above this limit at 39445 cm-1 lies Au W+Au 2 0 3 1 2 and this pair does provide a single 0 state. Linear extrapolation of the vibrational levels of state B gives 08 = 11800 cm-1 corresponding to a limit at 37480 em-1.This is a little below L. L . AMES AND R . F. BARROW 43 the value 39445 cm-1 but the extrapolation may give a low value of D in this case since it neglects a term +0.003 ( ~ + + ) 3 in G,(B). We conclude that state B is a 0 state correlating with Au 2S+Au 2 0 3 1 2 . The correlation of molecular states to atomic limits is illustrated in fig. 2. 40000~; 20000 2.0 40 6- 0 FIG. 2.-Potential energy curves for the states of A u ~ . Do is taken to be 18000 cm-1 and the curves are Morse functions. ELECTRON CONFIGURATIONS It remains to consider the electron configurations in these states. The ground state may be represented by 5dlo5dlo (ag6s)2 IZgC but this is undoubtedly too simple a representation as is shown by the fact that the bond strength in A u ~ is 51.5 kcal compared to 10.4 kcal in C s 2 which is also formally (ag6s)2 1Xl.This suggests that there is considerable d-s mixing in A u ~ . States A and B may then be the case c 0,' states arising from the configurations 5dlo o,"n~S,4a,2crU and 5d%,2n,36~o,27rw respectively. The expected anti-bonding character of the highest au orbital and the nearly non-bonding character of the highest nu orbital in these configurations is reflected in the vibrational frequencies and internuclear distances of states A and B. COVALENT RADIUS OF GOLD The covalent radius of gold in Au2 may be compared with the values obtained from the metal hydride 8 and from gold metal 9 in table 7. The value obtained from Au2 is in good agreement with the hydride value but considerably smaller than the rneta.Uk radius.TABLE 7.-vALUES OF THE COVALENT RADIUS OF AU A Au2 1.236 AuH- 0.300 1 -224 Au metal 1.339 44 GASEOUS AU2 MOLECULE One of us (L. L. A.) acknowledges the award of National Science Foundation Post-Doctoral Research Fellowship held in conjunction with an Honorary Ramsay Memorial Research Fellowship. We would also thank the Royal Society and the Science Research Council for grants. 1 B. Kleman S. Lindqvist and L. E. Selin Arkiv Fysik 1954,8,505. 2 J. Ruamps Comp. rend. 1954,237 1489. 3 J. Drowart and R. E. Honig J. Chem. Physics 1956,25 581. 4 P. Schissel J. Chem. Physics 1957 26 1276. 5 M. Ackerman F. E. Stafford and J. Drowart J. Chem. Physics 1960,33 1784. 6 J. Ruamps Ann. Physique (Paris) 1959 (13) 4 11 1 1. 7 A. Lofthus Spectroscopic Wavelength Standards (University of Oslo 1956). 8 U. Ringstrom Arkiv. Fysik 1964,27,227. 9 L. Pauling The Nature of the Chemical Bond (Cornell University Press 1960) p. 403.

ISSN:0014-7672    

DOI:10.1039/TF9676300039

出版商:RSC    

年代:1967

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. Intensity of the Carbonyl Stretching Modes in Certain Halo- genocarbonyl Derivatives of Chromium Tungsten Manganese Rhenium and Iron BY E. W. ABEL AND I. S. BUTLER Dept. of Inorganic Chemistry The University Bristol 8 Revised 21st Junuary 1966 The infra-red absorption intensities of the metal-carbonyl stretching modes have been determined for the following species Mn(CO)sI Mn(CO)sBr Mn(CO)sCl Re(CO)sI Re(CO)sBr [Cr(CO)sI]- [Cr(CO)sBrl- [cr(co)~c~l- fW(CO)sIl- Iw(co)~Brl- [w(co)sc~l- FHc0)412 EMn(Co)&l- [Mn(CO)4Brzl- fMn(C0)4LBrld [Mn(C0)4BrCl]- Mn2(Co)sI2 Mn2(Co)sBr2 Mn2(Co)sC12 Cr(C0)6 Mo(CO)6 and W(CO)6. The spectra are discussed and some force constants have been calculated.The spectrum of di-iodotetracarbonyliron has been assigned. The integrated intensities of the carbonyl stretching absorptions in metal carbonyl derivatives have received little attention when compared with the corresponding measurements in organic molecules such as amides and ketones,ls 2 but some interesting effects 3 ~ 4 have been reported. In addition to the points discussed in this paper it is to be hoped that the results set out will offer a check on further normal co-ordinate analyses and calculations of interaction constants for these compounds. EXPERIMENTAL The commercial group 6 hexacarbonyls were purified by sublimation and the other metal carbonyl derivatives were prepared by literature methods.5-10 Spectra were recorded with a Perkin-Elmer model 237 grating spectrophotometer pro- ducing a 0-10 mV output coupled to a Mark 111 Kent recorder.Recording was at the rate of 100 cm-l/rnin and one inch of chart paper corresponded to approximately 50 cm-1 of spectrum. The measured spectral slit width in the metal carbonyl stretch region was 4.3 mm (2.3 cm-1). Normally path lengths were 0.1 mm but for compounds of low solubility 1.0 mm cells were used. Extensive preliminary measurements indicated that these conditions produced the most reproducible values of extinction coefficients which also compared well with previous measure- ments. The cells used were new precision-path matched pairs ; sodium chloride and calcium fluoride windows were used with no observable differences in intensity values. Cell thick- nesses were checked from interference measurements and were found to be the nominal values rrt2 %.The spectra of the metal hexacarbonyls were obtained in hexane and the spectrum of di-iodotetracarbonyliron was recorded in both chloroform and hexane. All other spectra were recorded in chloroform and by using fresh solutions decomposition was negligible during the time of measurement. An exception to this was the halogenopentacarbonyl- metallate ions of molybdenum where it was suspected that decomposition was taking place in chloroform. The molybdenum results were therefore rejected as being insufficiently accurate. Generally spectra were recorded at 3-4 different concentrations to give transmittance over the range 15-85 %. Where possible four separate recordings of the spectrum were made for each concentration and the average values from these determinations was used to 45 46 CARBONYL STRETCHING MODES find In (To/T) and Avf in each case.Over the range of concentrations studied Beer’s law was found to apply to all the neutral and anionic species studied. The areas under the experi- mental bands were obtained in the region of &50 cm-1 from the band centre. This was done by cutting out the band (or extrapolated band) and weighing the paper which had been previously calibrated. The average value of a number of these determinations was used. Wing corrections were applied to all areas and then the integrated intensities were calculated by the methods discussed in the appendix. RESULTS Ramsay studied 11 the factors influencing the shapes of infra-red absorption bands in solution and concluded that the true shape of a single absorption may best be represented by the Lorentz equation.a In rf) = ( v - v0)’ + b2’ where vo is the position of the band centre and a and b are constants. Assuming a triangular slit function he established relationships between the true and apparent peak intensities the half-band widths and the slit widths. He then described three methods for the determination of the true integrated absorption intensity of an infra-red absorption band from experimental data. The first method involves the direct integration of the Lorentz equation a correction factor being applied for the use of finite slit widths. The other methods are extensions of the extrapolation procedures used by Bourgin 12 and by Wilson and Wells 13 for gases. The background to all three of these methods is outlined briefly in the appendix with particular reference to the way they were used in this work.Since the spectra were measured in the region 15-85 % transmittance the relative error in In (To/T) can be expected 14 to be less than 7 %. Further since the average of at least three or four measurements was used and sometimes up to eight the maximal error can be assumed to be less than 7 %. Under these conditions the relative error in the integrated intensities obtained by method 2 can be expected to be approximately 10 %. The observed integrated intensities for each separate measurement were in agreement with this but only the mean values are shown in the tables. The relative error in the individual values of the integrated intensities obtained by methods 1 and 3 are probably of similar magnitude as that in method 2.All three methods depend upon the assumption of the Lorentz type curve for the true band shape and also upon a triangular slit function. The accuracy of these assumptions is most critical in method 1. This depends upon measurements at say three points and has the advantage of rapidity. Defects of method 1 are that it is totally unsuitable for overlapping bands and even when used in lone bands a small deviation from the symmetrical shape can give rise to serious errors. Method 2 can be used satisfactorily for partially overlapping bands and further any inflection points are likely to be averaged out. Method 3 was only used in a small number of cases as a check and then values were found to be in agreement with those obtained from method 2.The integrated and specific intensities (integrated intensities per CO group) of the group 6 metal hexacarbonyls and di-iodotetracarbonyliron were obtained in n-hexane solution using method 2 in order that our results could be compared with those of Noack 3 for these compounds. It can be seen from Table 1 that in addition to the agreement of the intensities there is also good agreement for frequencies molar extinction coefficients and half-band widths. The spectra of all other species were obtained in chloroform. This was a far from ideal solvent,ls but was the only E. W. ABEL AND I . S . BUTLER 47 solvent suitable fo; both the neutral and ionic species and which was itself also free from absorption in the region of the measurement. cr(co)6 1989 (1987.5) 48,500 (52,000) 69,500 (-) 3.8 (3.7) 2.5 (-) 2765 (a) (2790) 461 (465) 1956 (1955) 1000 (1000) - - - - - 1958 (1957) 1000 (800) - - - - - 1952 (1952) 1000 (1200) - - - - - Mo(CO)a 1990 (19895) 53,800 (54,000) 78,500 (-) 3.7 (3.7) 2.4 (-) 3232 (b) (3005) 539 (501) W(CO)6 1983 (1983) 61,200 (56,000) 79,000 (-) 4.5 (4) 3.4 (-) 3322 (=) (3316) 554 (553) Results of Noack 3 in brackets for comparison value by method I 2751 by method I11 2692; ( b ) value by method 13039 by method 111 2985; value by method I 4140.by method 111 3207. DISCUSSION NEUTRAL AND ANIONIC HALOGENOPENTACARBONYLS The results in table 2 indicate that the molar extinction coefficients of the neutral halogenopentacarbonyls are greater than those for the corresponding anionic halo- genopentacarbonyls.Yet if specific intensities are used for a comparison of these two series the reverse result is noted. This anomaly was observed 3 in a comparison of the carbonyl stretch intensities for the species Ni(C0)4 and [Co(CO)4]-. In this paper intensity will refer to specific carbonyl intensity obtained from integrated absorption intensity determinations. The presence of charge on the anion would be expected to increase the polarity of the carbonyl groups and hence their absorption intensity resulting in the increase of peak area. Using a solvent like chloroform however would also lead to increased interaction between the carbonyl groups and solvent dipoles. This too would lead to band broadening and increased absorption intensity. However provided com- parisons of integrated intensities are made in the same solvent this solvent effect is made consistent throughout.Molecules of the type M(C0)sX have formal C4v symmetry for which group theory predicts three (2A1+ E ) infra-red-active CO stretching frequencies. The E vibration corresponds closely 16 to the Tip vibration of the hexacarbonyls M(CO)6 while the two A1 modes consist of the stretching mode of the unique CO group and the sym- metrical breathing mode of the other four CO groups (fig. 1). These modes have already been assigned from studies 16 17 of their qualitative relative intensities. As has already been pointed out,169 17 if the two A 1 modes did not couple only the A(:) mode would be allowed. The A(:) can gain intensity in three possible ways (a) deviation of the four planar CO from perfect planarity ; (b) mechanical coupling of the planar M(CO)4 system with the unique CO stretch; (c) electronic coupling via the d orbitals common to the n-bonding of both types of CO group.Whereas (a) and (b) depend upon distortion (c) does not. It has been qualitatively noted that the intensity of the A(;) mode varies considerably in relative intensity when compared with the E and 4;) modes of the same compound. We can now however make comparisons of the values of A(;) intensities between different molecules. We note P 00 Ymax (cm-1) A ( $ ) E A ( ) 2125 2044 2007 2133 2049 2004 2138 2053 2001 2145 2042 1990 2150 2044 1985 2045 1915 1856 2055 1921 1857 2058 1921 1856 2060 1917 1854 2063 1915 1845 2065 1913 1847 TABLE 2,-.4BSORF"ION INTENSITIES BY METHOD XI FOR THE M(C0)sX TYPES 8 (1. mole-1 cm-1) max A(:) E A(1) 930 7,100 2,270 430 7,030 1,990 210 6,560 1,720 530 7,930 1,890 220 8,460 2,060 540 4,510 1,290 250 3,430 990 170 3,340 940 410 4,690 1,310 250 4,670 1,250 210 4,750 1,270 Ex 10-2 E X 10-2 (1.mole-1 cm-2) (l.mole-l cm-2) per CO ~d (cm-1) 3 Av' (cm-1) 4. &Lax (I. mole-1 cm-1) A(;) E A ( ) A(?) E A(:) A ( ) E A ( ) A(?) E A(!) 1,060 7,320 2,300 6 12.5 21 5 12 20.5 85a 1247b 78lC 423 470 7.200 2,020 7 13.5 22 6 13 22 44d 1194' 6441 376 306 230 6,740 1.740 600 8,130 1,900 6.5 14 25 6 14 20 44" 1408 643 419 24' 1464 639 425 260 8,560 2,080 7 13.5 25 6 13 25 560 4,580 1,310 9 37 51 8 37 51 73.*1 2147 918 628 250 3,470 1,000 9.5 36 43.5 9 36 43.5 31 1592' 639 452 190 3,370 950 10.5 38 47.5 10 38 47.5 25" 1593 619 447 440 4,760 1,320 8.5 33.5 53 8 33.5 53 36 2073 990 620 8 36 51-5 26" 2129 887 608 270 4,720 1,270 250 4,800 1,280 9 35.5 51 8.5 35.5 51 23P 2190 907 624 9 12.5 21.5 8-5 12 21.5 218 1034 475 9 36 51-5 a 83 by method 1 ; * 1210 by method 111; 8 13 by method I11 ; d 45 by method I ; 11 19 by method I11 ; f 600 by method I11 ; a 30 by method I ; h 52 by method I and 40 by method 111 ; 29 by method I ; J 74 by method I ; k 36 by method I and 32 by method I11 ; 1 1530 by method I11 ; m 28 by method I ; n 52 by method I ; O 35 by method I ; P 29 by method I.2.49 VJ 2.57 cl 2.40 4 241 0 2.09 g E Z 0 m VJ 49 the contrast between the type (i) light metal-heavy halogen exemplified by Mn(,C0)51 and the heavy metal-light halogen (ii) exemplified by Re(C0)SBr. The respective values for specific intensities of the A'!) modes in these compounds are 8,500 and 2,400 1.mole-1 cm-2. Also in species with comparable mass characteristics the intensities of are similar despite presence of excess charge as the following pairs illustrate. Mn(CO)sI 7,500 [Cr(CO)sI]- 7,300 ; Re(CO)SBr 2,400 [W(CO)sBr]- 2,600 1. mole-1 cm-1 etc. E. W. ABEL AND I . S. BUTLER 7" A(!' E A(%) FIG. 1 .-Allowed carbonyl stretching frequencies of M(C0)sX and [M(CO)5X]- species (only one component of the degenerate E mode shown). In contrast to this the intensities of the E and A(:) modes for species with com- parable mass characteristics are very different. As might be expected the E mode is most strongly affected by the presence of excess negative charge and is in general roughly 50 % more intense than the E mode in the corresponding neutral species.The A(:) mode being due to only one absorbing carbonyl group is generally less affected. In order to rationalize these variations a considerable increase in exact structural knowledge of these compounds is required together with full normal co-ordinate analyses. TABLE TH THE COTTON SIMPLIFIED SECULAR EQUATIONS FOR M(CO)sX E = o TABLE 4.-FORCE CONSTANTS AND INTERAcTlON CONSTANT FOR THE AXIAL AND PLANAR CO GROUPS IN M(C0)sX SPECIES Mn(C0)sI Mn(C0)sBr Mn(C0)s C1 Re(C0)sI Re(C0) SBr Cr(C0)sI- Cr(C0)sBr- Cr(C0)sCl- M o (C0)SBr- W(CO)sI- W (C0)sBr- Mo(C0)sI- Mo(C0)SCl- W(C0)sCl- vmax (cm-1) A(!) E A ( ; ) 2125 2044 2007 2133 2049 2004 2138 2053 2001 2146 2042 1990 2150 2044 1985 2045 1915 1856 2055 1921 1857 2058 1921 1856 2061 1925 1857 2062 1924 1856 2063 1923 1850 2060 1917 1854 2063 1915 1849 2065 1913 1847 force constants (rndynelA) kl kz ki 16.37 17-29 0.21 16.32 17.39 0.22 16-28 17-46 0.22 16.13 17.38 0.27 .16-03 17-43 0.28 14.07 15.45 0.32 14.10 15.56 0.33 14.07 15.58 0.34 14.07 15.64 0.34 14.04 15.66 0.34 13.97 15.63 0.35 14-05 15.55 0.36 13-96 15.55 0.37 13.94 15.54 0-38 50 CARBONYL STRETCHING MODES Using Cotton’s 18-20 simplified secular equations for the M(C0)sX species (table 3) we have calculated the force constants for the axial (kl) and the planar (k2) CO modes.and the simplified interaction constant kt (table 4). A comparison of the force constants for the neutral and anionic species indicates the expected result that both kl and k2 are considerably lower for the anionic com- pounds. The availability of excess negative charge can also be expected to cause the higher interaction constant kt observed in the case of the anions.NEUTRAL AND ANIONIC DIHALOGENOTETRACARBONYLS The dihalogenotetracarbonylmanganates [Mn(C0)4X2]- and di-iodotetracarbonyl- iron all have cis-structure and formal C2tr symmetry. In such cases four infra-red active carbonyl stretching modes (2A1+ B1+ B2) would be expected.16P 18 The trans pair of carbonyls give rise to a weak A(:) mode and an antisymmetric BI stretching mode while the other two carbonyls give a symmetric A ( ) mode and an antisym- metric B2 mode of comparable intensity (fig. 2). FIG. 2.-Allowed carbonyl stretching frequencies of cis-X2M(C0)4 molecules. The spectra of Fe(CO)& in both chloroform and n-hexane solutions show three well-resolved bands with a fourth very weak band at lower frequency.A similar spectrum has been reported 3 in which it was suggested that the weak band might not be a fundamental and the real fourth peak is coincident with the strong one at 2086 cm-1 since this is much stronger than the corresponding peaks for the chloride and bromide. The weak band is probably due to a C13O mode. A spectrum involv- ing four peaks has been reported 21 in which there is a doublet with maxima at 2081 and 2086 cm-1. The positions of the three bands in chloroform solution have been accurately found 22 and assigned in order of decreasing frequency to the A( f) [A(; ),&I and B2 modes respectively. We have used the method of Cotton 18 to find the likely assignment. The three observed frequencies were used to calculate the force constants in the approximate secular equations (table 5) and then these were used to calculate the fourth frequency.The form of the secular equations together with the assump- tions that (i) ki>O and (ii) k2>kl require the A ( ; ) mode which is localized in the trans CO(2) groups to have the highest frequency. The assignments of the other three modes are not subject to any general restrictions and thus there are six possi- bilities (table 6). Of the six assignments only (3) gives k2 > kl ki > 0 and an acceptable value of the frequency for the fourth band. Thus the strongest band does indeed consist of two bands close together and confirms that the assignment of Horrocks,22 is correct viz. 2135 [A(:)] 2089 [ A ( ) B1] and 2068 cm-1 [&I. The intensities of Fe(CO)& together with values obtained previously 3 for the corresponding bromide and chloride are given in table 7.The A( and B2 modes would be expected to have roughly comparable intensities and this is indeed the case for the bromide and the chloride but for the iodide the intensity of the A( mode is boosted by the near degeneracy of the B1 mode and is much larger than that of the 8 2 mode. E. W. ABEL AND I . S . BUTLER 51 TABLE 5.-APPROXIMATE SECULAR EQUATIONS FOR L2M(C0)4 MOLECULES infra-red active approx. secular equations CO stretching modes \ I / M w o // 'L L B1 B2 A - = kl-ki P TABLE FO FORCE CONSTANTS FOR THE SIX POSSIBLE FREQUENCY ASSIGNMENTS IN Fe(CO)& assignment force constants calc. frequency of band c_____ kt the fourth no. A ( ) A ( ! ) B1 B2 ki k2 1. 2135 2089 - 2068 imaginary roots obtained 2.2135 2089 2068 I 17-75 17.67 0.20 2085 3. 2135 - 2089 2068 17.43 17.95 0.16 2080 4. 2135 - 2068 2089 17.94 17-93 0-33 2111 5. 2135 2068 2089 - 18.16 17.84 0.11 2114 6. 2135 2068 - 2089 17.87 17.05 0.25 2025 The force constants and assignments for the bands of the dihalogenotetra- carbonylmanganates are given in table 8 together with the force constants calculated for Fe(C0)4Br2 and Fe(C0)&12 using the data of Horrocks.22 The frequencies and the force constants kl and k2 of the anions are much lowered when compared to those of the corresponding neutral species due to the presence of excess negative charge. Also as expected kd is larger for the anions.18 TABLE 8 .-FORCE CONSTANTS CALCULATED FROM FREQUENCY MEASUREMENTS MADE IN CHLOROFORM SOLUTION Yrnax* force constants (mdyne/A) compound A ( ; ) 2078 2080 2089 2097 2131 2135 21 50 21 64 2087 2098 2104 B1 A ( ) BZ 2004 1983 1941 2005 1982 1941 2013 1987 1942 2019 1991 1939 2086 2062 2047 2089 2068 2108 2098.5 2074 2124 2108 2084 2031 2007 1973 2042 2008 1975 2047 2006 1977 kl k2 kr 15.48 16.75 0-26 15.48 16-77 0.28 15-50 16-91 0.27 15.47 17.03 0.28 17-09 17-90 0.17 17.43 17.95 0-16 17-53 18.26 0.16 17.69 18-52 0.15 15.92 17.07 0.20 15.96 17.25 0.21 16.00 17.35 0.21 * The assignment of the modes in the [M(CO)&Y]- and Mz(CO)gX2 species is A'(2) A" A'(1u) (0) The spectrum was recorded in n-hexane solution ; (b) data taken from Noack's paper 3.and A'(1b) and Bg) BI, B$? and B2* respectively. vmax (a-1) A($) B1 A':) B2 2135 2089 2068 2150 2108 209852074 2164 2124 2108 2084 2078 2004 1983 1941 2089 2013 1987 1942 2080 2005 1982 1941 2097 2019 1991 1939 TABLE 7.-INTENSITY DATA FOR Fe(C0)4X2 [ ~ ( c o ) & ] - AND [Mn(C0)4Brzl- ~ v t ( a - 1 ) E X 10-2 (I.mole-1 cm-2) (fz:)-; 8 a (1. mole-1 cm-1) A(:) B1 A ( ) B2 A(:) B1 A ( ! ) B2 A(:) B1 A':) B2 A(:) B1 A ( ) Bz A(;) B1 A ( ) B2 ~~~~~~) 3 Av" (cm-1) .) 8 (1. mole-' cm-1) max max 1,270 3,400 1,040 1,370 3,490 1,060 7 12.5 15.5 6 12 15 140 607 258 251 65 285 195 190 184 900 4,400 3,050 2,500 - - - - 4 5 5 6 - - - - 500 2,600 2,000 2,200 - - - - 6 6 5.5 7 - - - - 58 226 142 231 166 840 2,640 1,200 1,350 880 2,670 1,220 1,360 9.5 19 25.5 25.5 9 18-5 25 25 121 "652 350 471 399 410 2,320 1,260 1,560 430 2,340 1,290 1,570 11 19 16-5 25.5 105 18.5 16 25 56 537 225 570 347 * data of Noack 3 a 116 by method I ; 72 by method 11.TABLE g.-INTENSITY DATA FOR [Mn(C0)4IBr]- AND [Mn(C0)4BrCI]- E X 10-2 (1. mole-1 cm-1) 8nfax (1. mole-1 cm-1) AV; (cm-1) AV; (cm-1) E X 10-2 (1. mole-1 cm-2) 1. mole-1 ~ ' ( 2 ) A" lo) A'(1b) ~ ' ( 2 ) A" ~ ' ( 1 0 ) A'(1b) ~ ' ( 2 ) A" A'('") ~ ' ( 1 b ) ~ ' ( 2 ) la) A'(lb) ~ ' ( 2 ) 4" A'(1a) A'(1b) cm-2per co group 470 2130 1260 1350 510 2150 1280 1360 16 22 20 25 15.5 21.5 19.5 243 92O 582 193 480 348 250 1830 1020 1390 260 1850 1040 1400 9 20 14 25 8-5 20 13.5 24.5 33b 445 196 463 277 * 114 by method I ; 35 by method I. E. W. ABEL AND I . S. BUTLER 53 mode of the halo- genopentacarbonyls it might be expected that it will be affected in a similar manner by the size of the halogen atom. The local dipoles of the A(:) mode have their similar poles facing one another and hence there would be a large repulsion energy and this mode would be expected to have the highest frequency.17 The larger the halogen the more the two carbonyl groups deviate from coplanarity and consequently the intensity would be expected to increase while the frequency should decrease due to the relaxation in local dipole cancellation.This effect is well illustrated by the Fe(CO)& Since the A ( ) mode is in effect one component of the &la) A421 A‘ A’(1b) FIG. 3.-mowed carbony1 stretching frequencies of cis-XYM(C0)4 molecules. * x * x Bg) Bg) FIG. 4.- Allowed carbonyl stretching frequencies for the M2(CO)s& molecules assuming D2n symmetry (0 represents a halogen atom). TABLE ~o.-INTENSITY DATA OF THE Mn~(co)& MOLECULES Av’ 4 E x 10-2 1. mole-1 cm-2 E~ 10-2 par CO Ava 3 v * max compound (2) A 1 B1 A‘:’ B2 A‘:) B1 A‘:) Bz A‘:’ B1 A‘:’ Bz A”) 1 B1 A‘:) B2 group Mnz(CO)& 2087 2031 2007 1973 6 9.5 17 19 5.5 9 16.5 18.5 280 1060 550 939 354 Mnz(CO)aBrz 2098 2042 2008 1975 7 14 16 25 6 13.5 16 25 128 286 442 764 270 Mnz(C0)sClz 2104 2047 2006 1977 7 14 16 25 6 13.5 16 25 33 802 370 802 251 * using the assignment for the ciS-M(CO)& molecules.compounds and also by the [Mn(CO)&]- and [Mn(C0)4XY]- anions. The symmetry of the latter species is Cs and four infra-red active CO stretching modes (3A’+A”) would be expected for such a structure (fig. 3). The four modes are identical to those in the [Mn(CO)&]- species e.g. the A’(2) is analogous to the A(2) mode in fig. 2. These modes are similarly affected by the size of the halogen atom.In going down the series from the diodo- to the bromochloro-complex there is a distinct decrease in intensity accompanied by an increase in frequency of the high frequency band. and B2 modes of the [Mn(C0)4X2]- species are of comparable intensity as expected and the specific intensities of both the Fe(C0)qXZ and the [Mn(C0)&2]- The A( 54 CARBONYL STRETCHING MODES species decrease with decreasing size of halogen. This is also to be expected since the size of halogen will affect all four normal modes of vibration. The specific intensities of the anions are much greater (-50 %) than those of the neutral com- pounds. The greatest effect of charge is exhibited in the B1 and B2 modes. For the cis-M(C0)4XY species the four bands were assigned by analogy with the cis-M(CO)4Xz species (table 9).The A” and Af(lb) modes are of comparable intensi- ties and the specific intensities decrease with decreasing size of halogen. The structure of Mn2(CO)gBr2 has been investigated 24 by X-ray diffraction and found to consist of two Mn(C0)4Br units fused together through the bromine atoms giving the molecule overall D2h symmetry. It is to be expected that coupling between the CO stretching modes in one unit with those in the other will be negligible. There- fore the four infrared active Bl, Bzu and 2233 CO stretching fundamentals of the dimer may be regarded as analogous to the B1 B2 and 2A1 modes of the cis-M(CO)& molecules (fig. 4 and 2 respectively). It has been shown 20 that the treatment of the modes in the above manner is valid. The infra-red frequencies of the dimers are lower than those of the Fe(C0)4X2 compounds but higher than those of the [Mn(CO)&]- anions.This would lead us to expect specific intensities between the values obtained from those two species (table 10). decreases in intensity as the halogen becomes smaller due to the effect of decreasing repulsion forces between the halogen and the carbonyl groups. This effect has been noted25 qualitatively. The specific intensity decreases with decreasing size of halogen in an exactly analogous manner to that observed for the M(C0)sX and M(C0)4X2 species. The values calculated for the force constants (table 8) are as expected in between those calculated for the other two species. The weak high energy band A ( ! ) or APPENDIX THEORY OF INTENSITY MEASUREMENTS METHOD 1.-DIRECT INTEGRATION A working equation for the peak area may be derived.11 n K A = 2 - cl -Avt In ( 2)vmaxy where Avi is the measured half-band width and TO and Tare the incident and trans- mitted intensities at vmax.K is defined as In (Io/&max A v ~ - In (To/T)vmax A v ~ and values for are available 11 ’ in tables for a range of experimental values of S/AvZ and In (To/T)vm where S is the actual slit width.12 Using the tabled values for K all factors in the equation for A above are obtainable experimentally. METHOD 2.-ACTUAL MEASUREMENT OF ABSORPTION AREAS In this method the initial area of the band is measured over a range (v-VO) on either side of the band centre and then corrections made for the “wings” outside the E . W. ABEL AND I . S. BUTLER 55 measured range A1 and w are the measured and “wing” areas respectively.Values of x and 1v are available from tables for a range of experimental data.11 12 A = (x/cZ)(A~ + w). METHOD 3.-ZERO EXTRAPOLATION METHOD This method is similar to method 2 where at lim A = Al/cZ. Thus a plot of A I/cZ against cZ extrapolated to CZ = 0 gives A directly. As in method 2 A1 is corrected for “ wings ” before plotting. C l - r O 1 T. L. Brown Chem. Rev. 1958,58,581. 2 M. St. C. Flett PhysicaZ Aids to the Organic Chemist (Elsevier Publ. Co. New York 1962) 3 K. Noack Helv. chim. Actu 1962 45 1847. 4 W. Beck and R. E. Nitzchmann 2. Nuturforsch. 1962,176 577. 5 E. W. Abel and G. Wilkinson J. Chem. SOC. 1959 1501. 6 E. 0. Brimm M. A. Lynch and W. J. Sesney J. Amer. Chem. Soc. 1954,76,3831. 8 W. Hieber and G. Bader Chem. Ber. 1928,61 1717. 9 E. W. Abel I. S. Butler and J. G. Reid J. Chem. Soc. 1963,2068. 10 E. W. Abel and I. S . Butler J. Chem. Soc. 1964,434. 11 D. A. Ramsay J. Amer. Chem. SOC. 1952 74,72. 12D. G. Bourgin Physic. Rev. 1927 29 794 and 1928 32 237. 13 E. B. Wilson and A. J. Wells J. Chem. Physics 1946,14 578. 14 D. Asknes and G. Asknes Acta Chem. Scund. 1963 17 1262. 15 G. Bor Spectrochim. Acta 1962 18 817. 16 L. E. Orgel Inorg. Chem. 1962 1 25. 17 M. A. El-Sayed and H. D. Kaesz J. Mol. Spectr. 1962 9 310. 18 F. A. Cotton and C. S . Kraihanzel J. Amer. Chem. Soc. 1962 84,4432. 19 C. S. Kraihanzel and F. A. Cotton Inorg. Chem. 1963 2 533. 20F. A. Cotton Inorg. Chem. 1964,3 702. 21 C. C. Barraclough J. Lewis and R. S. Nyholm J. Chem. SOC. 1961,2582. 22 R. C. Taylor and W. D. Horrocks Inorg. Chem. 1964,3 584. 23 W. Hieber and H. Wirsching 2. unorg. Chem. 1940,245 35. 24 L. F. Dahl and C. H. Wei Acta Cryst. 1963 16 611. 25 M. A. El-Sayed and H. D. Kaesz Inorg. Chem. 1963 2 158. p. 189. E. W. Abel G. B. Hargreaves and G. Wilkinson J. Chem. Soc. 1958 3149.

ISSN:0014-7672    

DOI:10.1039/TF9676300045

出版商:RSC    

年代:1967

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. Ultra-Violet Polarization Ratios in Anthracene-Tetracene Mixed Crystals BY C.D. AKON AND D. P. CRAIG William Ramsay and Ralph Forster Laboratories University College London Received 31st August 1966 The visible absorption and emission spectra of tetracene in anthracene host crystal have been re-investigated and values of polarization ratio and crystal intensification factors recorded with the help of measured crystal thickness and tetracene concentration. The results are compared with theoretical expectations based on solution oscillator strengths and estimates of higher transition multipoles. The trend is correctly accounted for and the agreement for polarization ratios and intensification factors is reasonably good. Experiments on mixed crystals in which a host molecule is replaced by a guest with the same orientation of axes are of importance for theories of intermolecular inter- actions in molecular crystals.Difficulties over the treatment of electromagnetic retardation of the dipole-dipole interactions which are severe in pure crystals appear in mixed crystals in a much weakened form and there are experimental advantages from the fact that measurements can be made with relatively thick crystals in which the guest is present in high dilution. Mixed crystals of tetracene in anthracene provide a favourable example because the ultra-violet spectra of both host and guest are well known and adequate theoretical models are available. Advances in technique have made it necessary to record new measurements of the polarization properties of fluorescence and absorption in these systems.Some of the present results have already been briefly reported in part 1 and compared with previously available values3 The host anthracene crystals belong to space group P21/a and both fluorescence and absorption are measured with the electric vector of the light parallel and per- pendicular to the b crystal axis and the direction of propagation perpendicular to the ab plane. The extinction coefficient in absorption is different for the two directions of polarization of the light. The polarization ratio is defined as PR(b/a) = where ~b and are extinction coefficients for the band maxima with light polarized parallel and perpendicular to the b crystal axis. Similarly in fluorescence PR(b/a) = &/Ea where E is the intensity of the light emitted with the indicated polarization directions.Corresponding quantities integrated over the whole bands are of more fundamental significance. The definitions are then modified by replacing E or E by S&(ij)dij or SE(ij)dij where i j is the energy of absorption or fluorescence. In absorption the polarization ratio is then the ratio of oscillator strengths for absorption of the two electric vector directions of the light. With the assumptions that tetracene replaces anthracene by a simple substitution at a lattice site and that the directions of the corresponding molecular axes are exactly preserved we may calculate the oriented-gas polarization ratio for a transition of any given molecular polarization property. For the first absorption system of tetracene in which the absorbed light is polarized parallel to the shorter in-plane molecular axis the oriented-gas polarization ratio is 7.7 1 with the stronger com- ponent along the b crystal axis.Evidence in support of the assumption that the mixed 56 C. D. AKON AND D. P . CRAIG 57 crystal of tetracene in anthracene forms by precise molecular substitution is lacking but in a number of other and similar mixed crystals the correctness of the assumption has been shown by spin resonance studies of the triplet state of the impurity molecule.3 Measurements of polarization ratios for ultra-violet absorption and fluorescence give values different from the oriented-gas ratio both in pure and mixed crystals and the character and extent of these departures from expectation are the subject of the present investigation. EXPERIMENTAL The spectral measurements were made with a specially constructed single-beam recording spectrophotometer based on a Hilger-Miiller monochromator with photo-multiplier detection.Fluorescence spectra were recorded continuously across the spectrum but in absorption were obtained with point-by-point measurements. The device as a whole was linear with respect to light intensity within the limits used. The apparatus was calibrated in spectral response with a standard light source. Light was polarized by passage through a Glan prism with collimation to ensure that the divergence of the light beam was less than 4" of arc. The purity of the emerging polarized light was checked by the insertion of an accurately oriented second polarizing prism. Mixed single crystals were grown from dimethyl formamide by the method of Lipsett 4 by adding about 10-3 mole of tetracene for each mole of anthracene in solution.The anthracene used was B.D.H. blue fluorescence-grade zone-refined in 70 passes ; tetracene was repeatedly re-crystallized from benzene. Its extinction coefficient in cyclohexane at 275 mp was found to be 2.94 f0.05 x 105 in excellent agreement with a recent measurement in dioxane.5 Earlier literature reports invariably give a lower extinction coefficient probably on account of oxygen contamination. The crystals used were all of approximately the same thickness and were free from imperfections under microscopic examination. All had developed ub crystal faces. Crystal thickness was measured from the difference in height between the focal planes at the upper and lower surfaces of the crystal measured microscopically and corrected to true thickness using the refractive indices of anthracene of Sundararajan.6 Crystals about 200 p thick were used throughout the thickness measurement being accurate to about 5 %.The tetracene concentration was estimated spectrophotometrically by dissolving a known mass of the crystal in cyclohexane and measuring the optical densities of the solution at 310 and 275 mp. From the values of the extinction coefficients of tetracene and anthracene at the two wavelengths the percentage tetracene to anthracene can be calculated (for anthracene E at 275 mp 3-08 f 0 . 1 5 ~ 102 and at 310 mp 1-26 &O-04 x 103 ; for tetracene E at 275 mp as already quoted and at 310 mp 6 1/50 E of tetracene at 275 mp). The concentrations so found are accurate to about f8 %.Otherwise measurements of fluorescence and ab- sorption polarization ratios were made by standard methods. The polarizing prism and other optical components were not moved during the experiments. In order to eliminate errors due to polarization discrimination within the optics different polarization directions were observed by rotating the crystal between runs through 90" on a microscope stage. RESULTS A typical absorption spectrum is shown in fig. 1 and a table of results in table 1. The values quoted in table 1 are means of results obtained on two crystals each measured four times. The imperfect agreement between values obtained from band maxima and integrated band areas is mainly to be ascribed to the difficulty of allowing for background absorption which was troublesome even in apparently perfect crystals.The ratios of extinction coefficients measured at band maxima are therefore probably the more reliable. Values at 430mp are the least satisfactory on account of the absorption tail of the anthracene host crystal. The results in table 1 are compared with those of Choudhury and Ganguly2 for &b. The new values are higher; the agreement for the weaker absorption in the direction is within 10-20 % in extinction 58 ULTRA-VIOLET POLARIZATION I N CRYSTALS coefficient. Probably Choudhury and Ganguly's values were low on account of penetration of the crystal by a small component of light with the " wrong " polariza- tion. This can have a large effect on measurements of the intensities of strongly absorbing systems and must be avoided by rigorous experimental precautions to ensure that the incoming light is completely polarized._- 4 0 $-r h 3.0 3 4 73 2 0 0 .- $-r n I 0 0 2 2 0 0 0 23000 2 4 0 0 0 20000 21000 frequency (cm-1) FIG. 1 .-Typical absorption spectrum of tetracene in anthracene host crystal. Tetracene concentra- tion 1-03 x 10-3 mole/mole &8 % ; crystal thickness 176 p. TABLE 1 .-ABSORPTION BY TETRACENE IN ANTHRACENE SINGLE CRYSTAL l(w) v(cm-1) 'Xt fb't 'bIEa fblf 490 20,410 2 8 8 x 104 (2.23 x 104) 0.024 4-0 3.6 459 21,790 2-27 x 104 (1.72X 104) 0.023 3.9 3.7 430 23,260 1 . 0 5 ~ 104 ( 1 . 1 5 ~ 104) 0.012 3.1 3.1 * The uncertainty in the extinction coefficients and oscillator strengths is about f 12 %. Polariza- tion ratios in which the errors due to crystal thickness and concentration measurements do not arise should be better than A10 %.Bracketed values are those of Choudhury and Ganguly.2 ** oscillator strength. j- Values revised from those given in a preliminary communication 1 to take account of new values of extinction coefficients of rigorously oxygen-free anthracene solution on which the estimation of crystal concentration depends. We are indebted to Dr. Gad Fischer for new measurements. 0 il - 17000 18000 19000 20000 2lOOO frequency (cm-1) PIG. 2.-Fluorescence emission spectrum of tetracene in anthraame host. C. D. AKON AND D. P . CRAIG 59 Fig. 2 and table 2 show the results obtained in fluorescence. The values quoted are means of a large number of determinations carried out on several different crystals. A comparison with the results of Choudhury and Ganguly given in table 2 discloses values that are lower and closer to those obtained in absorption.TABLE 2.-FLUORESCENCE OF TETRACENE IN ANTHRACENE CRYSTAL mw) v(cm-1) EblE $Ebdvl$E,dv 532 18,800 4.6 f0-2 4.7 A10.2 (5.2) 57 1 17,510 5.0 f0.2 5.6 f0.2 (5.7) 495 20,200 4.4 f0.2 ** 4-9f0.2 ** (5.7) * ratio of maximum intensities. ** affected by re-absorption ; bracketed values are those of Choudhury and Ganguly.2 COMPARISON WITH THEORY A general understanding of the results may be had with the help of theoretical studies of the mixing of states of the guest molecule with those of the host by inter- molecular forces.7-9 Let us suppose that the guest-host interactions are the same as those of host and host implying not only accurate alignment of the guest on a site left vacant by a host molecule but also equal host and guest transition moments for corresponding transitions.Then if w is the difference between the excitation energy of the lowest transitions of guest and host i.e. the trap depth the transition energies in the mixed crystal are given by the values of E solving eqn. (l) where N is the number of lattice sites in the finite crystal block used to calculate the pure host energy spectrum e&) k being the wave vector. The N sites in the mixed crystal are occupied by N - 1 host molecules and one guest. The lowest of the energy levels from eqn. (1) applies to an excitation essentially localized in the guest (trap level) and the other solutions apply to delocalized or free excitons in the host. Presently we are concerned only with the trap level here well separated from all the others.We now re-write eqn. (1) with the energy variable e referring to the centre of gravity of the host band er where e(k) = e' + I&) 4 In expressions (2) Vpg is the interaction energy between the guest molecule at site p and hosts at sites q. For the trap level assumed widely separated from the host band we expand in powers of Z&)/e W = 1 - -z{ 1 + I@)/e + (I(k)/e)2 + . . .>. Ne k (3) Application of the closure properties of sums over the wave vector k gives for the leading term e = w+CVk/e+. . . which may be written approximately for large e e = w+cV&/w+. . . 4 4 (4) 60 ULTRA-VIOLET POLARIZATION I N CRYSTALS This agrees with the result of a straightforward application of perturbation theory in ref. (9) but depends on the assumed equality of the host-guest and host-host inter- actions.In the limit of perturbation theory result (4) applies with no such restriction. The appearance of the sum of squared interactions in expression (4) shows that the host-guest coupling falls off rapidly with distance and retardation effects can be neglected. For the same reason however consideration of higher multipole inter- actions should be included a problem not considered in earlier work. The calculation of polarization ratio depends upon the wave function for the guest molecule. These are obtained as in ref. (9) by consideration of the mixing of the first two excited states of the host with the guest. In table 3 the results of calculations are compared with experimental results ; the dipole calculations are those of ref.(9) while the effects of including higher multipole moments have been newly worked out by Dr. T. Thirunamachandran.10 Table 3 includes values for the intensiJication factors not so far defined. They are the ratios of the measured oscillator strengths to those calculated from the solution spectrum with the oriented gas assumption. They are thus indices of the degree to which intensity transfers are induced between different free molecule transitions under the influence of intermolecular forces. They depend upon the measurement of absolute absorption strengths in the crystal and are less accurately known than the ratio of measured intensities given by the polarization ratio. TABLE 3 .-CALCULATED AND EXPERIMENTAL POLARIZATION RATIOS AND INTENSIFICATION FACTORS PR PR 1 1 1 member (expt.1 pR (calc.A)* (calc. B)* (exp t .I (calc. A) (calc. B)* n = O 3.6 2.77 4.17 2.2 1.7 2-36 n = 1 3.7 2-68 4-10 1-5 1.5 2.42 n = 2 3.1 2.57 4.0 1.8 1.8 2.50 * calculation A based upon solution values of transition dipole moment and zero values of calculation B solution values of transition dipole moment and values of tetracene octupole progression higher multipoles. moment to fit the crystal spectrum of pure tetracene viz. 01 = 4eA3 03s = - 130eA3. t see table 1. The experimental intensification factors in table 3 have been calculated from the crystal intensities in table 1 and solution values of oscillator strengths for the successive absorption maxima of 0.0291 0.0398 and 0.0224. The experimental results fall between those calculated on the basis of purely dipole coupling and the basis including realistic values of higher moments.The agreement is generally satisfactory while however not favouring one or other basis decisively. The work has been sponsored in part by Air Force Cambridge Research Labora- tories OAR through the European Office of Aerospace Research (OAR) United States Air Force. C . D. A. acknowledges the award of a postgraduate travelling Fellowship by Messrs. I.C.I.A.N.Z. 1 C. D. Akon and D. P. Craig J. Chem. Phys. 1964,41,4000. 2N. K. Choudhury and S. C. Ganguly Proc. Roy. SOC. A 1960,259,419. 3 C. A. Hutchison and B. W. Mangum J. Chem. Phys. 1961,34,908. 4 F. R. Lipsett Can. J. Phys. 1957 35 284. 5 R. S. Becker I. S. Sin& and E. A. Jackson J. Chem. Phys. 1963,38,2144. 6 I. K. S. Sundararajan Z. Krist. 1936,93 238. 7 G. F. Koster and J. C. Slater Phys. Reus. 1954 95 1167. * D. P. Craig and M. R. Philpott Proc. Roy. SOC. A 1966 293,213. 9 D. P. Craig and T. Thirunamachandran Proc. Roy. Suc. A 1963,271,207. 10 T. Thirunamachandran 1966 private communication.

ISSN:0014-7672    

DOI:10.1039/TF9676300056

出版商:RSC    

年代:1967

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. Vibrational Relaxation of Hydrogen Chloride Deuterium Chloride and Hydrogen Bromide at Room Temperature BY MARGARET G.FERGUSON AND A. W. READ* Chemistry Dept. Edinburgh University Received 26th August 1966 The vibrational relaxation times of HCI DCl and HBr have been determined by a spectrophone method. Shorter limits to the relaxation times are 1.1 x 10-2,1 x 10-2 and 1-5 x 10-3 sec respectively. These results agree better with vibration-rotation theory than with vibration-translation theory. The results for HCl is compared with high-temperature shock-tube data. Little is known about the vibrational relaxation of the hydrogen halides. Observa- tions of the infra-red emission from shock-heated gas indicate that the relaxation times of hydrogen chloride and hydrogen bromide at 2000°K are several orders of magnitude shorter than predicted by theory.1 The discrepancy is greater than any previously found for diatomic molecules and it is therefore important to know the relaxation times of these molecules at lower temperatures.Because of their high vibrational frequencies the room temperature equilibrium vibration populations are very low and prevent the use of the ultrasonic interferometer.2 This limitation does not apply to the optic-acoustic method and we have investigated the vibrational relaxation of HC1 DCl and HBr using the spectrophone developed during work on carbon monoxide.3 The basis of this method is that vibrationally excited molecules with long relaxation times (> 10-3 sec) will lose energy both collisionally and radia- tively. The time constant of the radiiative process which is known from the absorp- tion intensity provides a time scale by which the efficiency of the collisional process can be determined.EXPERIMENTAL A description of the spectrophone and experimental arrangement are given elsewhere.3 In the present work the final amplification of the spectrophone signal was by a General Radio Company Tuned Amplifier and Null Detector type 1232A. During the experiments the Melinex diaphragm was replaced frequently since the gases used even when pure and dry slowly attacked the metal coating. MATERIALS Hydrogen chloride was prepared (i) from m C 1 and H2SO4 and (ii) by reacting HCl with conc. H2S04. In both cases the gas was dried with H2SO4 and P2O5 condensed at - 196" degassed and distilled into the spectrophone. Hydrogen bromide was obtained from a cylinder (Matheson Co.minimum purity 99.8 %) dried over P2O5 and further purified as for HCl. Deuterium chloride was prepared by reacting Sic14 with D20.4 Infra-red analysis showed that the gas contained 10-20 % of HCl. This arose from an exchange mechanism with the * present address Central Electricity Generating Board Regional Research and Development Department Kirkstall Power Station Leeds 4. 61 62 RELAXATION I N HYDROGEN HALIDES water adsorbed on the walls of the gas-handling system despite precautions to eliminate such contamination. After several preparations in the same system the percentage of HCl was greatly reduced. In the later runs DC1 was obtained from a cylinder (Merck Sharpe and Duohme) condensed at - 196" degassed and distilled at - 120".In all cases a new sample was prepared for each experiment. RESULTS A gas sample was allowed to diffuse rapidly into the baked degassed spectrophone and the initial signal found. During a period of several hours the signal rose to a steady value. This rise is caused by impurity molecules from the walls which shorten I-SxlZ- a 3 2 J 0.20 UP (cm Hg1-1 FIG. 1.-Relaxation times in HCl and DC1 as a function of l/pressure 0 HCl results ; A DCI results. Line is drawn for a relaxation time of 1.1 x 10-2 sec. FIG. 2.-Relaxation times in HBr as a function of l/pressure. Line is drawn for a relaxation time of 1.5 x 10-3 sec. M. G . FERGUSON AND A. W. READ 63 the relaxation time until all the vibrational energy is lost by collision. Measurements with mixtures of HC1 and H2 (10 %) which would be expected to have short relaxation times showed no such rise with time indicating that the effect is not due to attack on the diaphragm.From the initial and final signals the relaxation time z was calculated using the expression 3 initial signal/final signal = l/~/(l/r + l/Trad). The radiative lifetimes TABLE RELAXATION TIMES AT 290°K (APPROX.) FOR HCl DCl AND HBr compound radiative lifetime ( S d relaxation time (SW) HCI 0.03 >1.1 x 10-2 DCl 0.12 -1 x 10-2 HBr 0.15 > 1.5 x 10-3 (Trad) were derived from absorption intensities using the method of Penner.5 The absorption intensities for HCl and DCl were taken from measurements by Benedict Herman Moore and Silverman,6 and for HBr from Babrov.7 The relaxation times as a function of l/pressure are shown in fig. 1 and 2 and the values for 1 atm.are given in table 1. The large scatter of the DC1 results is almost certainly due to impurity effects since it is extremely difficult to obtain DC1 without small varying amounts of HCI. DlSCUSSION Because of the difficulties of obtaining pure gas samples all the relaxation times are shorter limits to the true values this effect being most important at lower pressures. At higher pressures some re-absorption of an emitted quantum may take place ; this will again lead to a shorter relaxation time. The magnitude of the re-absorption effect has been investigated by Doyennette and Henry,s who found that the spectrophone value of 0.8 sec for the relaxation time of carbon monoxide 3 should be increased to 6 sec to take account of re-absorption. The relaxation times in table 1 are therefore quoted as lower limits.The experimental relaxation times may be compared with those cdculated by vibration-translation theory9 Values of a were obtained by method B of Herzfeld and Litovitz,lo using the Kreiger potential function as amended by Monchick and Mason.11 The theoretical results are given in table 2 where they are compared with the experimental values. TABLE 2.-THEORETICAL RELAXATION TIMES AT 290°K FOR HCl DCl AND HBr compound a (em-1) "theor. Ttheor.lrexpt. HCl 5 . 8 4 ~ 108 6.5 <59x 102 DCl 5 . 8 4 ~ 108 1.6X 10-2 < 1-6 HBr 5.9x 10s 5.1 x 104 ~ 3 . 4 x 107 Whilst the theoretical value for DCl is nearly correct those for HC1 and HBr are too long even allowing a factor of 5 for re-absorption effects. The same theory gives good results for such gases as CO 0 2 and N2 all of which have long relaxation times at room temperature.Possibly with the hydrogen halides vibrational energy 64 RELAXATION IN HYDROGEN HALIDES is relaxing by some other mechanism so that the vibration-translation theory does not apply. Such a mechanism could be that suggested by Cottrell and Matheson,12 involving vibration-rotation energy transfer. This process is expected to be most efficient for molecules with low moments of inertia and correspondingly high rotational velocities. The hydrogen halides are such molecules the hydrogen atom effectively rotating about the much heavier halogen atom. The vibration-rotation mechanism has been treated theoretically by Moore 13 and the results of his treatment expressed as ratios are given in table 3 where they are compared with the ratios derived from vibration-translation theory and the experimental results.TABLE 3.-RATIOS OF RELAXATION TIMES AT 290°K ratio rib-trans. theory vib-rot. theory expt. T H C ~ ~ D C ~ 4.1 x 102 1.1 x 10-1 -1 rHCI/THBr 1.3 x 10-4 2.5 7.3 The agreement between theory and experiment is much improved particularly for the ZHCI/ZH~~ ratio. The theory assumes that rotational energy is continuous which may not be justified for the hydrogen halides where the rotational levels are ( T°K)-l 13 FIG. 3.-Relaxation times in HCl as a function of (temperature)-1'3 0,3-0 results 14 ; @,1-0 results 1 ; A present work. separated by 10-20 cm-1 and a more refined treatment might give better agreement with experiment. Results for the 3-0 transition on HCl have been obtained by Borrell and Gutte- ridge 14 using a shock tube.The v = 3 level of HC1 would be expected to relax rapidly to v = 1 by resonance collisions of the type HCl(u = 3) + HCl(v = O)+HCl(o = 2) + HCl(u = 1) HCI(U = 2)+ HCl(tl = 0)+2HCl(~ = 1). M. G . FERGUSON AND A . W. READ 65 Thus the 3-0 relaxation time should be effectively that of the 1-0 process which will be much slower than the resonance processes. The results of Borrell and Gutteridge are plotted in fig. 3 for comparison with the present result. The approximate 1-0 results for HC11 are also plotted and the line is drawr according to the translation-vibration theory. It appears that the shock tube results do not extrapolate towards the low temperature result. We thank the S.R.C. for a maintenance grant to M.G. F. 1 P. Borrell Chem. SOC. Spec. Publ. no. 20 (Academic Press 1966) p. 263. 2 T. L. Cottrell Int. Znst. Chem. 12th Conference 1962 (Interscience Publications New York 3 M. G. Ferguson and A. W. Read Trans. Faraday Soc. 1965 61 1559. 4 A. E. de Vries and F. S. Klein J. Chem. Physics 1964 41 3428. 5 S. S. Penner Quantitative Molecular Spectroscopy and Gas Emissivities (Addison-Wesley 1959). 6 W. S. Benedict R. Herman G. E. Moore and S . Silverman J. Chem. Physics 1957 26 1671. 7 H. J. Babrov J. Chem. Physics 1964,40 831. 8 L. Doyennette and L. Henry J. Physique to be published. 9 T. L. Cottrell R. C. Dobbie J. McLain and A. W. Read Trans. Faraaay Soc. 1964,60,241. 10 K. F. Herzfeld and T. A. Litovitz Absorption and Dispersion of Ultrasonic Waves (Academic 11 L. Monchick and E. A. Mason J. Chem. Physics 1961 35 1676. 12 T. L. Cottrell and A. J. Matheson Trans. Faraday Soc. 1962,58,2336. 13 C. B. Moore J. Chem. Physics 1965 43 2979. 14 P. Borrell and R. Gutteridge private communication. 1964). Press 1959).

ISSN:0014-7672    

DOI:10.1039/TF9676300061

出版商:RSC    

年代:1967

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. Ultrasonic Absorption Properties of Solutions Part 1 .-Dilute Solutions of Diethylamine in Water BY M. J. BLANDAMER D. E. CLARKE N. J. HIDDEN AND M. C. R. SYMONS Department of Chemistry The University Leicester Received 21st July 1966 The ultrasonic absorption properties of dilute aqueous solutions of diethylamine at 0 and 25" are characterized by a single relaxation time this being associated with the equilibrium RzNH$HzO + R2NH2+OH. Comparison is drawn with the data for solutions of t-butanol where no such equili- brium is detected. i. - An important feature of aqueous solutions is the significant increase in sound absorption measured by the ratio alf2 where a is the amplitude absorption coefficient and f the frequency which accompanies the addition of polar compounds such as alcohols or amines to water.1.2 At a fixed frequency and temperature the absorption is a function of liquid composition reaching maxima in the water-rich sy~tezns.3~ 4 Although attempts have been made to identify the absorption properties in terms of equilibria between either hydrogen-bonded entities and free molecules or between aggregates of the two components,4 5 these models are not generally satisfactory. In particular such treatments do not account for the insensitivity of a/f2 to the addition of t-butanol to water over the range 0.04> x2> 0 where x2 is the mole fraction of alcohol2 In view of the implications of this observation for the structural modifica- tions induced in water by added solvents,6* 7 the sound absorption of aqueous solu- tions containing diethylamine has been investigated over a comparable concentration range and this has revealed an important difference between the two systems.EXPERIMENTAL Solutions were prepared by volume at room temperature using distilled water and reagent- grade amine. Further purification had no effect on the results. All measurements were made on freshly prepared solutions. SOUND ABSORPTION MEASUREMENTS The absorption coefficient was measured using a pulse technique over the range 1.5- 230 Mc/sec. The two instruments one ranging from 1-5 to 28.5 and the other from 30 to 230 Mc/sec were essentially as described elsewhere.*-lo Thermostat units covered the range - 20 to + 45".Solutions were continuously stirred during measurement on the high- frequency apparatus. For both instruments signals were passed through a continuously variable attenuator and the liquid sample comparison being made between the resultant signal and a reference signal from the oscillator. The instruments record a straight line whose slope gives the change in path length in the liquid relative to a change in attenuation of the signal in liquid cell the external attenuation being automatically varied to maintain constant signal in the receiver. Hence the sound absorption coefficient at each frequency is obtained. In practice the average of five slopes is employed in the calculation. The procedure is repeated at each of ten frequencies (1.5,4.5 7-5 13.5 28.5 30 70 110 170 and 230 Mc/sec) and the results recorded on a plot of a / f 2 against log f.66 BLANDAMER CLARKE HIDDEN A N D SYMONS 67 ANALYSIS OF RELAXATION CURVES The variation of a/f2 with frequency can often be expressed in terms of a single relaxation frequency fc and two parameters A and B characteristic of the system (eqn. (1)). The A- parameter is related to the strength of the relaxation p = Auf, where u is the velocity of sound and the B-parameter contains contributions from the classical viscosity of the liquid and any other relaxing process having a high relaxation frequency. The data were fitted to eqn. (1) using a least-squares programme for an Elliott 801 computer which gives A B and& together with a/f 2 calculated from these derived parameters. In many systems however the differences between observed and calculated relaxation curves are far greater than the experimental error.The data are then re-examined in terms of two relaxation frequenciesf,, andf, (eqn. (2)). Since eqn. (2) alf = A m + (f/fc)l+ B (1) involves two more parameters than eqn. (l) a better fit between calculated and observed relaxation curves is expected. However the systematic trends in fCl and f with variations in temperature and solute concentration suggests that these derived parameters are not an artefact of the analysis. EXPERIMENTAL ERRORS Under favourable circumstances the experimental error in a/f 2 is approximately k2 %. However where the intensity is low the error is greater for the data at 1-5,4-5 and 30 Mc/sec due to the difficulty of measuring small changes in attenuation.The estimated error in a/f2 at 1.5 4.5 and 30 Mc/sec is 515 f 3 and f7x 10-17 sec2cm-1 respectively. At 1.5 and 4.5 Mc/sec a correction must also be made for an apparent increase in absorp- tion arising from diffraction effects. For dilute solutions it is assumed that this correction is equal to that for the pure solvent. At higher concentrations (>5 mole % approximately) this assumption is not valid due to significant differences between the bulk properties of the solvent and solution such as density sound velocity etc. This can lead to an uncertainty of up to f15 % in the correction to be applied to the observed absorption coefficient. Con- sequently at these higher concentrations an additional error of 3~60 and f3.5 x 10-17 may be involved at 1.5 and 4.5 Mc/sec respectively.Although most of the results concerning the amine solutions refer to concentrations below x2 = 0.05 the limits of error for alf2 at 1.5 Mc/sec remain significantly greater than at the other frequencies and hence these data have been omitted in the calculation of the re- laxation parameters. RESULTS The relaxation parameters for diethylamine in aqueous solution at 0 and 25" over the concentration range O<x2<0-05 are summarized in tables 1 and 2. In those systems where the molarity of amine is less than unity the relaxation curves are satisfactorily analyzed in terms of a single relaxation process characterized by A0 and fco table 1. At concentrations of amine where x2 > 0.07 a second relaxation (A1,fcl A2 fc and B) is detected. At intermediate concentrations it is difficult to decide between the two equations for the relaxation curve and so the derived parameters from both procedures are listed tables 1 and 2.Both A0 andf, increase with increase in amine concentration and for a given amine concentration A0 increases with decrease in temperature. At 25" the mean of the B values over the range of amine concentration O<c< 1 is 26 x 10-17 which is close to that for water at the same temperature.11 This shows that there are no new relaxation processes sensitive to ultrasound at high frequencies. 68 ULTRASONIC ABSORPTION IN ETHYLAMINE + WATER TABLE 1 .-RELAXATION PARAMETERS FOR THE ULTRASONIC ABSORPTION OF DILUTE AQUEOUS SOLUTIONS OF DIETHYLAMINE FROM ANALYSIS FOR SINGLE RELAXATION FREQUENCY amine conc. molarity C 0.002 0.002 0.01 0.01 0.01 12 0.02 0.028 0.04 0.04 0.06 0.10 0.10 0.25 0.30 0.50 0-50 0.90 1.0 1.0 1 -24 1 *24 2-25 2.25 2.93 2.93 mole fraction x2 0-000036 0.000036 O*OoO18 0.00018 0.0002 0.00036 O.OOO5 0.00072 0.00072 040108 04018 0.0018 0.00455 0.0056 0.0096 0.0096 0.01 76 0.0197 0.01 97 0.025 0.025 0.05 0.05 0.07 0.07 temp."C 0 25 0 25 0 0 0 0 25 0 0 25 25 0 0 25 0 10 25 0 25 0 25 0 25 1017 A, 94 57 113 52 112 115 111 128 43 134 128 65 62 127 131 72 1 62 122 58 1 52 71 293 183 1690 327 sec2 cm-1 1017 B~ 48 21 46 24 57 48 60 47 21 51 58 28 29 67 75 22 80 35 38 88 28 159 12 270 129 sec2 cm-1 relaxation frequency 106fc sec-1 10.5 5.8 18.3 13.4 12.5 24 -4 23.0 33.4 57.2 32.0 41.0 48-5 80.5 64.5 56.9 143 60.7 129 137 139 242 81.6 69.1 50.5 88.9 relaxation strength 10%0 -142 -050 -298 -105 0202 -403 -368 -617 -370 -618 -761 *48 1 *760 1-21 1.1 1 1.60 1-52 2-46 1 -27 1.93 1.59 3.41 7.30 8-64 14.4 TABLE 2.-RELAXATION PARAMETERS FOR THE ULTRASONIC ABSORPTION OF DILUTE AQUEOUS SOLUTIONS OF DIETHYLAMINE DERIVED FROM ANALYSIS FOR TWO RELAXATION FREQUENCIES 1017 loaf relaxation 1017 A2 106fc2 relaxation 1017B temp."C sec2 cm-l sw-i strength sec2 cm-l sec-l strength x2 102M 102p2 S N 2 CI-n-l 0.025 0 42 26.1 ,172 128 119 2.39 75 0.05 0 101 37.3 6.37 226 110 4.20 131 0-05 25 1 77 4.5 ,131 190 235 7.30 10 0.07 0 726 17.6 2-16 1200 84.9 17.2 144 0.07 25 1473 0.96 -228 325 115 6.10 99 a analysis includes data for absorption at 1.5 Mclsec. ANALYSIS OF RELAXATION PARAMETERS The relaxation parameters are analyzed in terms of equilibrium (i) ki + k - i - (C,HS),NH+M,O=(C,H,),NH + OH ( 0 the equilibrium constants 139 14 K at 0 and 25" being summarized in table 3.If the BLANDAMER CLARKE HIDDEN A N D SYMONS 69 activity coefficients of the various species is assumed to be unity the two rate constants are given by eqn. (3) where a is the degree of dissociation and c the total amine concentrations. (3) The relaxation frequency for equilibrium (i) is given 15 in terms of the two rate con- stants and the product ac in eqn. (4) K = k l / k - l = a2c/(l -m). 271 fc = kl +2ack- TABLE 3.DERIVED PARAMETERS FOR ACID-BASE EQUILIBRIUM FOR AMINES IN AQUEOUS SOLUTIONS temp. O0 25' amine diethylamine k-l,l. mole-1 sec-1 1 . 5 6 ~ 1010 1 . 5 6 ~ 1010 kl ss-1 2.0 x 107 o . 6 ~ 107 K 1. mole-1 0 . 7 8 ~ 10-3 2 . 6 ~ 10-3 K 1. mole-1 0 . 8 7 ~ 10-3 1.1 x 10-3 AV cm3 mole-1 27.3 19.1 monomethylamine kl sec-1 k-l,l.mole-1 sec-1 dimethylamine kl ss-1 k-l,l. mole-' sec-1 trimethylamine kl sec-1 k-l,l. mole-1 s e d 1 . 6 ~ 107 3.7 x 1010 1 . 9 ~ 107 3.1 x 1010 0.14~ 107 2.1 x 1010 a this work; b ref. (13) and (14); c ref. (19 table IV la; d sound absorption; e &dispersion. I 103 x 2ac FIG. 1 .-Dependence of relaxation frequency for the acid-base equilibrium for diethylamine in aqueous solution at O" 0 ; and 25"C 0 on 2ac where a is the degree of dissociation and c the total amine concentration. Hence a plot offc against ac gives the two rate constants fig. 1. At low concentra- tions the plot is reasonably linear but with increase in concentration especially at low temperatures deviations are observed. This stems from the increasing contribu- tions to the absorption from other relaxations having comparable frequencies and the 70 ULTRASONIC ABSORPTION I N ETHYLAMINE 4- WATER difficulties of analyzing the relaxation curves for these systems.The results are given in table 3 the error in kl being greater than that for k-1. The variation of relaxation strength p with concentration is given by eqn. (9 where r = a(1- a)/(2- a) ; AYis the difference between the volumes of products and reactants and /3 is the isothermal compressibility equated here to that for the pure p = Avf' = n(AV)2crlBRT ( 5 ) 103cr FIG. 2.-Dependence of relaxation strength p for the acid base equilibrium for diethylamine in aqueous solution at 0" 0 ; and 25"C 0 on cr where I' equals a(1- a)/(2- a); a is the degree of dissociation and c the total amine concentration. solvent.16 The variation of p as a function of cT is plotted in fig.2 the slope yielding A V at 25 and O" table 3. The zero intercept and the increase in p with increase in cT is in agreement with the trends expected if an equilibrium of the form shown in eqn. (i) were responsible for the absorption at low amine concentrations. DISCUSSION Equilibrium (i) involves a proton transfer between water and amine. Reactions of this class have been extensively investigated by Eigen and co-workers.15 Their kinetic data were derived from sound absorption and E-dispersion measurement. The latter technique only gives information for equilibria involving both ions and non- conducting species. Their results for mono- di- and trimethylamine in aqueous solutions at 25" are given in table 3. The rate constants evaluated here table 3 are similar.The trends in both kl and k-1 with change in temperature are consistent with a relatively temperature-insensitive diffusion-controlled ion-recombination and a temperature-dependent rate constant for ionization kl increasing with increase in temperature. Previously the lack of any significant change in the absorption of water accompany- ing addition of t-butanol over the range O<x2<0-04 was tentatively interpreted in terms of a clathrate model.3 The contrast between this insensitivity with the marked concentration dependence of a/'2 for aqueous solutions of diethylamine arises from BLANDAMER CLARKE HIDDEN A N D SYMONS 71 the acid-base equilibrium in the latter system. When x2 > 0.09 at 25" the extrapolated relaxation frequency for the proton transfer is greater than 300 Mc/sec and hence is no longer detected except as an increase in the B term.The new relaxation detected at low frequency is assigned to a process similar to that detected for aqueous t-butanol. We thank Imperial Chemical Industries Limited for the loan of equipment and the Science Research Council for maintenance grants. 1 D. Sette Encyclopedia of Physics (Springer-Verlag 1962) vol. 11 part I. 2 C. J. Burton J. Acoust SOC. Amer. 1948 20 186. 3 M. J. Blandamer D. E. Clarke N. J. Hidden and M. C. R. Symons Clzem. Comm. 1966,342. 4 J. H. Andrae P. D. Edmonds and J. F. McKellar Acoustica 1965 15 74. 5 R. 0. Storey Proc. Physic. SOC. 1952 65 943. 6 F. Franks and D. J. G. Ives Quart. Rev. 1966 20 1. 7 E. M. Arnett and D. R. McKelvey Record Chem. Progr. 1965,26 185. 8 J. H. Andrae and P. L. Joyce Brit. J. Appl. Physics 1962 13,462. 9 P. D. Edmonds V. F. Pearce and J. H. Andrae Brit. J. Appl. Physics 1962,13 551. 10 J. H. Andrae and P. D. Edmonds J. Sci. Instr. 1961,38,814. 11 J. M. Pinkerton Proc. Physic. SOC. B 1949 62,286; Nature 1947 160 128. 12 M. Eigen and K. Tamm 2. Elektrochem 1962 66 107. 13 D. D. Perrin Dissociation Constants of Organic Bases in Aqueous Solution (Butterworths 14 W. C. Somerville J. Physic. Chem. 1931 35 2412. 15 M. Eigen and L. DdMaeyer Technique ofOrganic Chemistry vol. 8 part 2 (ed. Friess Lewis and 16 Handbook of Chemistry and Physics (Chemical Rubber Publishing Co. Cleveland 42 edn. London 1965). Weissberger) (Interscience New York 1963) chap. 18. 1960).

ISSN:0014-7672    

DOI:10.1039/TF9676300066

出版商:RSC    

年代:1967

数据来源: RSC