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.

ISSN:0014-7672    

DOI:10.1039/TF9343000024

出版商:RSC    

年代:1934

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. 30 CONCERNING THE (ClOJx RADICAL GENERAL DISCUSSION. Mr. C. F. Ooodeve (London) said: I am inclined to agree with Birkenbach and Goubeau’s explanation of the reaction between iodine and AgClO, in ethereal solution. All of the observations recorded follow readily from the assumption that perchloric acid and a per- chlorate of ether are formed in equivalent amounts. Beyond the doubtful question of the oxidising power in respect to HI, Gomberg and Gamrath offer no evidence to indicate the formation of any other compound. We must conclude, therefore, that the existence of (C10,) ~ is unproven. It may be of interest to mention here that the existence of another new oxide of chlorine has been definitely established.Mr. Todd, working in our laboratories, has shown conclusively that chlorine hexoxide, identified first by Bodenstein, Harteck, and Padelt, exists entirely as chlorine trioxide in the gaseous phase. The molecular weight was determined by isolating a small quantity of the vapour in a quartz bulb and determining the pressure before and after heating the bulb to a red heat. Previous experiments showed that the vapour was completely decomposed a t this temperature and gave three volumes of oxygen to one of chlorine. Four determinations gave (within one per cent.) a doubling of the pressure. The molecule must, therefore, contain four atoms. It has also been found that an equilibrium between the liquid and gaseous phases is set up very rapidly, and that the equilibrium pressure at room temperature is about 8 mm. C10, is moderately stable at room temperature, and it is doubtful whether it can any longer be called a free radical. The existence of chlorine trioxide has been postulated by many workers, and its isolation and the results of a study of its properties, which will be published in full in the near future,@ will, it is hoped, play some part in the elucidation of the interesting reactions of the oxides of chlorine. S Nature, p. 514, 30th September, 1933.

ISSN:0014-7672    

DOI:10.1039/TF9343000030

出版商:RSC    

年代:1934

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. ON SULPHUR MONOXIDE. BY HEINRICH CORDES AND PETER W. SCHENK. (Communicated in German by PROF. K. F. BONHOEFFER and transhated by G. H. G. NEVILLE. Received 27th July, 1933. Sulphur monoxide, SO, is formed in an electric discharge in sulphur dioxide, or, better, in a mixture of sulphur vapour and sulphur dioxide a t low pressures.l Victor Henri found a band system lying between 2500 a. and 3900 A. in the emission spectrum of the discharge which he attributed to SO.The SO formed in the discharge may be pumped off from the discharge, and by the application of a condensed discharge of about 20 KV. under suitable conditions nearly pure SO may be obtained a t a pressure of about 10 mm.3 When cooled in liquid air sulphur monoxide gives a red condensate, which on evaporation decomposes completely with the separation of elementary sulphur and leaving only SO, in the gas phase. The condensate behaves as the anhydride of this sulphuric acid. A quantitative analysis of the gases pumped off from the discharge tube, based on the decomposition of the condensed com- pound into sulphur and sulphur dioxide when warmed, gives the ratio of oxygen to sulphur as I : I. The absorption spectrum shows a band system which converges towards shorter wavelengths lying between 3400 A.and 2500 A.4 The linear extrapolation of the convergence limit gives a value of 7-03 volts, indicating a dissociation of SO into a normal sP sulphur and an activated lD oxygen atom. The readings with which the absorption spectrum appears permits the detection of SO down to very low pressures. At room temperature SO is a gas which may be kept for some days in dry vessels. Decomposition is favoured by organic substances (tap grease) and water vapour. Similarly, the rate of decomposition is increased by rise of temperature. At 100' C. a strong decomposition is noticed after a short time, at 180' practically all SO has decomposed after one minute. SO reacts vigorously with metals, forming sulphides.At room temperatures SO does not react with oxygen ; the union of the two gases occurs in the electric spark. SO reacts with water, sulphur separat- ing, and with aqueous alkali it forms a reducing liquid which decolorises indigo and which is to be described as a solution of sulphoxylate or hyposulphite. In the short ultraviolet a photochemical decomposition of SO sets in. With the aid of a modified Topler pump, in which a football bladder distended with air in a flask replaced the mercury of the Topler pump, SO may be compressed to pressures of about 50 mm. Hg. A higher compression cannot be attained SO does not react appreciably with rubber. 1Peter W. Schenk, 2. anorg. allg. Chem., 211, 150, 1933. V. Henri, F. Wolff, J . Physique el Rud., €0, 81, 1929.H. Cordes and Peter W. Schenk, 2. anorg. allg. Chem., 213, to be published H. Cordes, 2. Physik, to be published shortly. shortly. 3132 ON SULPHUR MONOXIDE because of the considerable decomposition of the compound. SO differs with regard to different adsorption media. Silica gel causes an immediate decomposition ; as SO disappears in the mass, SO, is formed. Activated charcoal adsorbs SO slowly, and on subsequent heating not SO, but solely SO, is set free. The ready spectroscopic detection of SO permits the investigation of a number of chemical reactions with regard to the formation of SO. In the reaction between thionyl chloride vapour and metals with low heats of formation of their oxides compared with their chlorides (silver, antimony, sodium), SO is f ~ r m e d . ~ Metals with higher heats of formation of their oxides react with the formation of the metal oxide and sulphur di~hloride.~, On the other hand no SO can be detected in the de- composition of sodium hyposulphite, sodium thiosulphate, and sulphur sesquioxide and similarly the reaction of H,S with SO, gives no SO. 5 Peter W. Schenk and H. Platz, 2. anorg. allg. Chem., to be published shortly. * Vergleiche auch E. Gruner, 2. anorg. a&. Chem., au, 393, 1933.

ISSN:0014-7672    

DOI:10.1039/TF9343000031

出版商:RSC    

年代:1934

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. 32 ON SULPHUR MONOXIDE GENERAL DISCUSSION. Professor Lowry (Cambridge) said: I t would be interesting to know whether SO had the same magnetic properties as 0,. Professor Mecke (Heidelberg) said: May I ask Dr. Cordes how accurate he thinks his determination of the convergence limit i s ? I call attention to the fact that the value given by him (7'03 V.) is exactly the same as in the case of the oxygen molecule. Thus the dissociation energies of both compounds are alike.This is quite interesting, for one would expect a value lower than that of oxygen, being between I 18 Cal. (0,) and 100 Cal. (SJ. As to the nature of the SO radical I would refer here to my remark in the discussion on the paper of Steiner. Professor Bonhoeffer (Franizfurt a.M.) said: May I answer to the question of Professor Lowry concerning the magnetic behaviour of SO. It seems to me that in this case the method just mentioned by L. Farkas is especially suitable. I t should, therefore, be investigated whether the para-ortho hydrogen conversion is catalysed by the presence of SO. That would tell us immediately whether SO in the ground level is paramagnetic or not. I think that either Farkas or Cordes will do that.Professor Sugden (London) said : Would not spectroscopical in- vestigation give sufficient information on the paramagnetic behaviour ? Professor Bonhoeffer said : Certainly, if the investigation would be finished. Dr. E. J. B. Willey (London) said : The decomposition of sulphur mon- oxide on liquefaction is so much the reverse of what generally happens, that I venture to ask Dr. Cordes if he has an explanation of it. Can i t be due to an interaction of sulphur monoxide molecules one with another, or to a surface reaction which is so strong that it proceeds rapidly in spite of the low temperature?-in the latter case we would not expect the gas to be so stable at room temperatures. Professor Paneth (London) said: I am not quite sure whether decomposition of an unstable gas a t the moment of condensation is quite such a rare occurrence as Dr.Willey seems to think. One could quote, for instance, several of the hydrides, which are quite stable in€3. CORDES AND P. W. SCHENK 33 the gaseous state, and undergo partial decomposition in the process of liquefaction, Lead hydride has so far only been prepared in the gaseous state, and not the slightest traces have survived liquefaction. I agree with Dr. Willey that the reason for these decomposition processes is to be seen in the catalytic influence of the wall or, a t a later stage, of the products of decomposition. Dr. H. J. EmelCus (London) asked if the smell of sulphur monoxide had been identified with that noticed in the phosphorescent combustion of sulphur, and if i t would be possible from absorption spectrum intensity measurements to estimate the amount of the monoxide formed under these conditions.Dr. Oliver C. de C. Ellis (Shefield) said : I am very greatly in- terested in this paper, because a problem pressing upon the flame- investigators of The Safety in Mines Research Board is the inhibition of ignition ; and one of the very few exampIes of inhibitory action that is not a mere dilution is a reaction where, as I should judge, this radicle SO is almost certainly formed. I wish these authors, since they could so readily apply to the matter an experimental technique that is already highly developed, would verify that. " The fact is "-if I may quote dangerously from The Admirable Crichton-that the ignitibility of mixtures of air with the vapour of carbon disulphide is greatly diminished by the presence of small quantities of ethylene. This was discovered by Frankland.' He found that either hydrogen or carbon monoxide, if mixed with small amounts of carbon disulphide, would take fire a t a glass test-tube containing oil at 2 1 0 O C.; though coal-gas would not do so, because, though i t contains carbon disulphide before its purification, i t also contains ethylene ; and a minute trace of ethylene would destroy in any mixture that great ease of ignitibility which the presence of carbon disulphide confers upon it. The only explanation so far advanced is that of Dixon : * that in such mixtures the carbon disulphide oxidises first to carbon monosulphide and sulphur dioxide, and that a t the surface of the solid aggregates (of empirical formula CS) in suspension, the chemical processes of combustion become more active ; ethylene, acetylene, or nitrogen peroxide in the gas-mixture change the history of the oxidation, probably " by condensing on the surface of the CS a t an early stage, and so preventing its action as a nucleus." This explanation does not claim completeness or finality; and any mechanism of inhibition is of intense interest to those of us who seek any suggestive parallel or analogy that may lead to the prevention of explosions of methane and air in the pit. Chemical News, VI., 3 , 1862 ; Collected Works, 540. *Fuel, IV, 401, 1925, et alibi. 3

ISSN:0014-7672    

DOI:10.1039/TF9343000032

出版商:RSC    

年代:1934

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.

ISSN:0014-7672    

DOI:10.1039/TF9343000034

出版商:RSC    

年代:1934

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.

ISSN:0014-7672    

DOI:10.1039/TF9343000039

出版商:RSC    

年代:1934

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. 13.118 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.

ISSN:0014-7672    

DOI:10.1039/TF9343000040

出版商:RSC    

年代:1934

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. 5 2 STABILITY O F THE ORGANIC FREE RADICALS THE RELATION BETWEEN CHEMICAL AND PHYSICAL THEORIES OF THE SOURCE OF THE STABILITY OF THE ORGANIC FREE RADICALS. BY C. K. INGOLD (London). For comparison with Huckel’s treatment of this problem, and with the related calculations of Pauling and Wheland,l I recall the theory advanced by Burton and myself some years ago This chemical theory, although qualitative, is in some respects more general than the physical theories, and it collates a wider range of data.Furthermore, i t was the first theory of free radicals to utilise the now familiar ideas of non- localised electron bond functions and of resonance energy, so that its general conceptual basis is really identical with that of the recent more quantitative theories. In summarising the earlier theory, I shall con- tinue to use the system of nomenclature and notation developed in con- nection with the general theory of organic chemical reactivity. For the necessary explanation, and for an indication of the relationship between the free radical theory and the general theory of reactivity, reference may be made to the paper which I read a t a recent Chemical Society discussion.s 1 J . Chm, Physics, I, 362, 1933. 3 J . Cham. Soc., 1120, 1933.PYOC. Leeds Phil. SOC., I, 421, 1929.C. K. INGOLD 53 The theory of free radicals which I propose to summarise proceeds in three distinct steps. The first deals with the preliminary question of the source of the stability of the cation and anion corresponding to a hydrocarbon radical such as triphenylmethyl. In the second step, the treatment is generalised to include the neutral triphenylmethyl radical and other more complex hydrocarbon radicals. The third step involves further generalisation permitting the inclusion of radicals which are not hydrocarbons and may not even be based on a hydrocarbon framework. The primary consideration is the existence of a special form of de- generacy, and therefore of a corresponding loss of energy through re- sonance, associated with the class of formally analogous systems which is illustrated inter alia in all tautomeric structures.This principle is regarded as of very general significance in the theory of organic chemical reactivity, and in particular it is considered the driving force of all taut- omeric change. Thus the anion of the prototropic system and the cation of the anionotropic system, illustrated in the following formulae, are degenerate and, when produced from either isomeride, a t once pass into their stable mesomeric forms containing the distributed bond functions : Unperturbed forms (unstable) . Mesomeric Ions (stable) . Unperturbed forms (unstable) . Ion of Prototropic System. 0 0 R3 R'>2 R2 CH=C{ R4 0 R' 0 P R3 Z>C=CH-CC( R4 R Ion of Anionotropic System.0 R' n- R3 RZ >C-CH-C<R, 0 R ' R3 >C- CH- C< R4 R2 In the original paper the stabilising action of the perturbation was illus- trated by the analogy of a spreading macrophysical charge, and the un- certainty principle was cited as the ultimate justification for the con- ception of an unlocalised duplet. These ideas have become widely familiarsed since 1929 and we may therefore directly proceed with the present application. So long as attention is confined to hydrocarbons the primary qualitative consideration is that the energy of resonance must always be increased by an extension of the system which provides new unperturbed forms and new perturbation mechanisms. Thus the energy value of a degeneracy should be increased as we pass from the simple triad ion to a pentad or a heptad ion.Even in the benzyl ion the number of perturbation mechanisms and distributed proper functions is considerable as the following formulae indicate, and it is evident that these numbers become much greater in the benzhydryl ion, and much greater still in the triphenylmethyl ion :54 STABILITY OF THE ORGANIC FREE RADICALS Anion Bemyl Ions ; Examples of Unperturbed Forms. n n These then are the lines on which we sought to account for the degree of stability observed in the triphenylmethyl anion and cation. The preceding remarks relate only to perturbations which can be associated with the tautomeric displacement of electron duplets, and, when the dissociation considered has an ionic character (e.g. in triphenyl- methyl chloride and potassium triphenylmethide) the significance of such duplet-displacements is evidently the primary consideration.I t is a well-known consequence of the octet principle that the direction of mutually dependent tautomeric displacements must all be consistent in a given form of the system. When, however, it is desired to take neutral dissociation into account, the theory can no longer be expressed in terms of undivided duplets, and a new rule is therefore required con- cerning the direction of displacement of the electrons. This rule, which likewise follows from the principle of maximal octet preservation, is that coupled electrons always move in divergent directions, one electron remaining attached to each of the sharing atoms. The significance of this rule in relation to the triphenylmethyl radical is that perturbation mech- anisms analogous to all of those which are involved in the degeneracy of either one or other ion must co-exist and must all be coupled together in the degeneracy of the radical. The necessity for this can readily be made clear by an analysis of the situation. Let us, for example, single out the process whereby a dissociation-condition is transferred from C, to Corno and examine the function to be fulfilled by the CaCom0- electrons.The following formulae show that the behaviour of the C,Cofiho-duplets can be represented in the case of each of the ions by a single operating arrow, but that in the case of the radical both arrows are required, one operating on each of the component electrons, if octets are to be preserved elsewhere in the molecule than at the seat of the dis- sociation-condition. similarly in the case of a para-transition the two operating arrows of each ion become four in the case of the radical : TYP? of Transition.Process. Ions. Radical.C. K. INGOLD 5 5 Evidently the degeneracy of the neutral radical is of a very high order, and it is important that this should be so because the loss of energy has in this case to be comparable with the energy of rupture of a homopolar linking. The reason why aryl groups are so peculiarly well adapted for the production of stability in a radical into which they are substituted is quite clear : for whereas most groups by reason of their constitution and special polarity are virtually only one-way conductors of electrons (even if they are conductors at all), aryl groups permit conduction in both the directions which together are necessary for the degeneracy of the neutral radical. Moreover since, in the absence of disturbances such as are considered in the next paragraph, radical stability must follow the degree of complexity of the degeneracy, a basis becomes available for the qualitative prediction of the relative stabilising effects of different aryl groups in triarylmethyl hydrocarbon radicals.The following sequence was thus predicted, and has been verified to the extent indicated by the work of Gomberg and Schlenk. ORDER OF EFFECT OF ARYL HYDROCARBON GROUPS IN PROMOTION OF RADICAL STABILITY. Theory (illustrative) :- 9-Phenanthryl > a-Anthryl > a-Naphthyl > #I-Naphthyl > p-Diphenylyl > m-Diphenylyl > Phenyl.Found (Gomberg, Schlenk) :- a-Naphthyl > #I-Naphthyl > p-Diphenylyl > Phenyl. Finally it is necessary to introduce the reflection that the stabilising efficacy of degeneracies of the type considered must, in general, depend not merely on the number of perturbation mechanisms, but also on the facility with which those mechanisms actually operate. For example, it has been indicated that in the triphenylmethyl radical each phenyl group is required to conduct electrons in both the directions which separ- ately are characteristic of the two ions, and it is now necessary to enquire which of these two sets of processes most effectively limits the stabilising action of the degeneracy. The answer to this is obtained by reference to the ions.The tercovalent carbon anion is known to be intrinsically more reactive and less stable than the corresponding cation, as is shown, for example, by the electron-donating character of polarised ethylene. It must be concluded that the efficacy of the three phenyl or other groups in promoting the stability of a substituted methyl radical must be limited primarily by their capacity to perform that function whereby they con- fer stability on the corresponding anion. Therefore, within limits, the introduction into the aryl group of a substituent calculated to increase the stability of the anion by facilitating electron-absorption, even al- though it might decrease the stability of the cation, should nevertheless increase the stability of the neutral radical.The most striking example of this effect is provided by the stability of the trinitrotriphenylmethyl of Ziegler. In the cases of the bivalent nitrogen and the univalent oxygen radicals opposite conditions prevail, Here the related anions are more stable than the cations, and accordingly electron-releasing substitutents should promote radical stability. This also is in accordance with known results.56 STABILITY OF THE ORGANIC FREE RADICALS ORDER OF EFFECT OF SUBSTITUENTS IN ASSISTING PROMOTION OF RADICAL STABILITY. Radicals R,C 0 [R,C@ less stable than R,C'] p-NO, . C,H,. > (Ziegler). C6H5 ' Radicals R2N @ [R,N' less stable than R2N p-Me,N . C,H, , > p-Me0 . C6H4. > (Wieland). C6H5 @ Radicals RO [RO@ less stable than RO"] o-Me0 .C,H, , > (Goldschmidt). C6HS The theory of the hydrazyls differs from that of the simpler nitrogen radicals in that the stability of what might have been a highly unstable cation is augmented by the provision of a degeneracy which is inde- pendent of any aryl substituent. The result is a balance between the requirements of electron release and absorption, and, therefore, the way in which to increase the stability of a neutral hydrazyl radical by sub- stitution is to introduce, within limits, either an electron-releasing group, or an electron-absorbing group, or, better still, a group of each kind. This is the rule to which Goldschmidt's results conform, as the following table indicates. The electron-releasing groups are arranged on the left in the known order of their electron-releasing power, and the electron-absorbing groups are arranged similarly in order a t the top of the table.It follows that an increase in the stability of the radicaI should be observed on passing either downwards in the table or to the right, and there are some thirteen determined relationships between neigh- bouring pairs of compounds available to exemplify this requirement : ORDER OF EFFECT OF Radicals R2N. N R 0 SUBSTITUENTS IN ASSISTING PROMOTION OF RADICAL STABILITY. a Anion R2N . NR relatively stable, Unperturbed cation R26? &X unstable. Mesomeric cation R,N . NR relatively stable. Unperturbed cation R,N : NR unstable (3 & @ P IC. K. INGOLD 57 Goldschmidt’s results (Ar,N . NAc = type A ; ArAcN . NAr = type B) :- P-NO a- p-Br- p-H- p-Me- p-MeO- p-Me2N- - Increasing electron-absorption - +. Acet yl. Benzo yL Picryl. Increasing Dissociation -+ d .r. Y -+ Experimental relationship (arrow points to more stable radical), Key{ - Not investigated. I t is evident that this chemical theory is very closely related to the physical theories of Huckel and of Pauling as, indeed, the latter author has already remarked, and that up to a point each theory may act as a translation of the other according to whether depiction or description is most desired; but my main reason for once again drawing attention to the chemical theory is that a wide purview extenuates its qualitative character. Thus, it is not, like the physical theory, confined effectively to hydrocarbons; also i t brings out the relation between radicals and their ions ; chiefly, however, it brings the phenomena of the stable free radicals into intelligible relation with those other fields within the general theory of organic chemical reactivity from which they have hitherto been regarded as detached. In conclusion, it may be said that the feeble stabilising action of alkyl groups is not really intelligible on any present theory, but that this and other circumstances seem to suggest the existence of factors of resonance dependent on inductive, as well as on tautomeric, electron displacements.

ISSN:0014-7672    

DOI:10.1039/TF9343000052

出版商:RSC    

年代:1934

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. C. K. INGOLD 57 GENERAL DISCUSSION.* Dr. N. K. Adam (London) said : The spatial arrangement of the three phenyl groups round the central carbon atom in triphenylmethyl appears interesting, in view of the fact that in certain known cases where one valency of carbon has apparently disappeared, the remaining three valencies are found to be co-pIanar at I ~ o O , instead of directed towards the corners of a regular tetrahedron.Hexamethylbenzene has been shown by Mrs. Lonsdale to have all the carbons in one plane; and in graphite, the sheets of hexagons, presumably of typical aromatic structure as mellitic acid is formed by oxidation, also show a co-planar * On Dr. Huckel's paper (p. 40) ; see also Prof. Ingold's contribution (p. 52).STABILITY OF THE ORGANIC FREE RADICALS arrangement of the co-valencies, the fourth valency electron being apparently loose, since there is metallic conduction through the crystal.There is some resemblance, though it may be only superficial, between the structures of graphite and of triphenyl methyl, If attention is fixed on one carbon in graphite, three valencies lead to three aromatic hexa- gons; if we break all the bonds attaching these rings to others, and satisfy each of these broken linkages with an atom of hydrogen, we are left with triphenyl methyl. I wonder if the mathematical theory can give any indication whether the Van der Waals' forces between three phenyl groups on one carbon are likely to force the three valencies into one plane; also whether there is any necessary connection between a co-planar arrangement of three valencies and the disappearance of the fourth.Experimental study, either by X-ray analysis of solid compounds or by an attempt a t resolution of substituted triphenyl methyls, might be feasible. Possibly the three valencies are only distorted from their usual tetrahedral angle a part of the distance required to render them co-planar; one may hazard the suggestion that there may even be a quantitative connection between the strength of the fourth valency and the degree of departure of the three valencies from the usual direction. Professor J. E. Lennard-Jones (Cambridge) said : In connection with Dr. Huckel's paper, it might be of interest to observe that single layers of graphite might be regarded as large aromatic molecules, consisting of a network of benzene rings in juxtaposition.Each carbon is sur- rounded by three immediate neighbours, the angles between the links being 1 2 o O Presumably along these links there are the usual a-localised bonds, which account for three of the valency electrons of each carbon atom. The fourth electron of each carbon may be in what Huckel calls a p~ orbital, which is mainly concentrated above and below the carbon nucleus on a line passing through the nucleus and perpendicular to the plane of the layer. These electrons may be regarded as forming non- Iocalised bonds, and may pass easily from nucleus to nucleus. They are similar to the conduction electrons of a metal, and may give to graphite its well-known properties of conductivity. In the conventional language of chemical valency, the links of graphite would have to be written in the way shown in the figure, the dotted line representing 3 , two-thirds Each layer of a bond.will form a complete set of paired I electrons, and may be regarded as a large satur- / ated molecule. The interaction between SUC- ,' '\\ /' ' ' "', cessive layers will then be of the van der Waals' This is borne out by the large distance between successive layers (3.41 A. units), which is the same order of magnitude of distance to which inert gas atoms approached in the solid state. (The nearest distance between Argon atoms is 3-84 A.) This type of interaction between layers explains the ease with which succes- sive layers glide over each other. If this view of the electron structure of graphite is correct, it should be possible to establish by the X-ray analysis of the electron density that there is an electron maximum (corresponding to the pH-electron) on each side of a plane of nuclei.(Communicated): In connection with the above remarks on the electronic structure of graphite, Dr. Huckel has since kindly informed . ' .,- type.C. K. INGOLD 59 me by letter that he has also considered the same problem in some detail. He agrees with the picture drawn of electron bonds in each plane, but believes that between planes there are probably valency forces as well as Van der Waals’ forces. I agree that this is likely, but a t interatomic distances of 3.4 A. valency forces are usually weak, while Van der Waals’ forces are comparatively strong. Eisenschitz and London 1 have shown, for instance, that a t interatomic distances greater than 3.8 A.the valency forces between hydrogen atoms are less than the Van der Waals’ forces. Only calculation can settle which is the more important in graphite. Dr. E. Huckel (Stuttgart), in reply (communicated) : The conception of Ingold, according to which the stability of radicals like triphenyl- methyl is due to a “ degeneracy ” of a great number of tautomeric forms covers better the theoretical treatment of Pauling and Wheland than my The method of approximation given by Pauling and Wheland (the so-called Heitler-London method) in addition to providing an important mathematical simplification, which explains the significance of the concept of tautomeric forms and the effect of resonance between them, is essentially the same and gives the same results as that one of the two methods used by myself in my first paper on the benzene prob- lem.4 This method is there called method I.I have given up the use of this method further, for two main reasons. Firstly, the method was incapable of accounting for the peculiar behaviour of ring systems con- taining six p,-electrons. Secondly, it has proved that in case of per- turbations (substitutions) the method gives results which cannot be brought into accord with experiment.5 Therefore I used further another method of approximation, which is derived from Herzberg, Hund, Bloch, and others. This method was called method 11. in my first paper.* Mulliken calls i t the method of molecular orbitals. This method was able to give an account for both the points mentioned in which method I.failed to succeed. In method 11. the tautomeric forms and the de- generacy between them lose their importance. I believe that for theoretical calculations method 11. will also in other cases prove more adequate than the method based on the use of the tautomeric forms. -4s to the stability of the anion and cation of triphenylmethyl and other radicals, and also in regard to the connection between constitution and reactivity, some considerations will be found in some earlier paper^.^^^ I did not try a treatment as to the influence of substituents on the stability of free radicals, not only because of the difficulties in- volved in this problem, but also for the reason that quantitative experi- mental data on the influence of substitution on dissociation energy, entropy-factor and on the influence of the solvent are wanting.Further, 21t is to be noted that these tautomeric forms do not represent states of definite energies. States of definite energies arise from these by a phenomenon of resonance. Therefore the tautomeric forms can be considered as states and as degenerated from the standpoint of a peculiar method of approximation only. SNeither the conception of Ingold nor the paper of Pauling and Wheland were known to me when writing my paper. Added in $woof: By an oversight I omitted to mention that “ method 11.” was first used in a quantitative manner by Lennard- Jones on treating the electronic structure of diatomic molecules. (Trans. Far. SOC., 25, 600, 1929.) 2. PhysiR, 60, 491, 1930. E. Huckel, 2. Physik., 70, 204, 1931. Ibid., 72, 310, 1931 (Theory of induced polarities in benzene.) “bid., 76, 628, 1932; 83, 632, 1933.60 THREE DIMENSIONAL MODELS quantitative data on the stability of cations and anions are not avail- able. Nevertheless the considerations of fngold seem to give a qualitative explanation for the relations involved in these problems, although the concepts used do not seem to me always to be able to be defined exactly. With respect to the remarks of Dr. Adam I would say : In case of co-planar arrangement there is not a complete disappearance of the fourth valency. This has been discussed for hexaphenylethane and ethane in my original paper.7 In case of triphenylmethyl it is not the van der Waals’ forces which stabilise the co-planar arrangement, but the gain in resonance energy. As to graphite the existence of “ residual valencies ” between the hexagon planes can be established by theoretical considerations, taking into account the resonance between adjacent atoms in neighbouring hexagon planes. 7 E. Htickel, 2. Physik., 83, 648, 1933.

ISSN:0014-7672    

DOI:10.1039/TF9343000057

出版商:RSC    

年代:1934

数据来源: RSC

摘要:

60 THREE DIMENSIONAL MODELS THREE DIMENSIONAL MODELS OF THE POTENTIAL ENERGY OF TRIATOMIC SYSTEMS. BY C. F. GOODEVE. Received 15th September 1933. Solid models have been used for many years to represent systems of three variables both for lecture demonstrations and practical purposes. Such models have been particularly useful for phase rule diagrams. Re-cently a number of models have been made in these laboratories to re-present the potential energy of systems of three atoms as a function of the atomic distances. These models have proved of great value in demon-strating atomic reactions of various types the modes of vibration of triatomic molecules,l etc. The method of their manufacture is simple and such models may be found useful in other mathematical or physical problems.The models were carved from solid rectangular blocks of laminated plaster made by Messrs. Henry Hartley & Company,8 and the following details of construction have been kindly supplied by them. A number of wooden frames were made each of which enclosed a space 12 ins. square and 9 in. deep. The first frame was laid on a flat surface and the space filled with plaster of paris which was levelled to the top of the frame. Before the plaster in the frame had finally set a film of red-coloured plaster was brushed over the face. A second frame was set on top of the first, filled with fresh plaster levelled brushed with coloured plaster and so on until the complete block was made. The models shown in the Plates were made from blocks of sixteen laminations.The coincidence of each frame one upon another was obtained by means of an external frame-work into which each of the individual frames fitted. The blocks so made were found to be suitable for all kinds of working such as sawing drilling planing scraping. There was little tendency to chip or to split a t the laminations except where narrow parts were being carved. Where this occurred repairs were readily made by means of additional plaster or by use of secotine. When dry they could be scraped or polished with sand-paper. lModels with springs have been made by Kettering Shutts and Andrews (Physic. Rev. 36 531 1g30) to show the vibration of polyatomic molecules. Wood Lane London PLATE I. PLATE 11 PLATE 111. PLATE TV. [To facc page 61 C. F. GOODEVE 61 The carving was carried out in the following way.A diagram of the equi-potential contour lines was first made as described below. This was transferred to the top face of the block by photographing the diagram, projecting the negative by means of an enlarging camera and tracing the contour lines on this face. The potential energy-distance curves for the diatomic molecules (products of dissociation) were then traced on the sides concerned (see Fig. I). The block was placed on the bed of a machine drill into which had' been fitted a $-in. drill made from a wood bit. The FIG. 1.-The system of two oxygen atoms and one carbon atom. drill stop was fixed at a position such that the maximum depth of the drill corresponded to one of the laminations and the corresponding contour line was drilled out to this depth.The process was repeated with a number of other contour lines. Large bulks were however conveniently removed with a large-toothed saw. The model was then finished with a chisel and a plane and finally scraped smooth. The numbers and letters were stencilled on. Fresh polishing and lettering were readily done when necessary. The System of Three Hydrogen Atoms. In this way the four blocks shown in Plates I. to IV. were made. In Plate I. is shown a model of the potential energy of the system of three hydrogen atoms plotted against the distances separating the atoms. The zero of the spatial dimensions is taken at the position of the central hydrogen atom and the two horizontal axes represent the respective distances of the two outer hydrogen atoms from the central atom.The potential energy is given by the vertical axis. The contour lines were taken directly from the paper by Eyring and Polanyi and in this case 2. Physik. Chem. 12B 279 1931 62 THREE DIMENSIONAL MODELS were calculated only for the resonance forces between the atoms. In this as in all other models of three atom systems it is necessary to fix one degree of freedom so that the spatial configuration can be repre-sented in two dimensions. It is generally most convenient to fix one of the angles of the system and in this case the three atoms are fixed on a straight line. At any other angle the potential energy is higher than that given by the model. All of the conclusions obtained by Eyring and Polanyi can be demon-strated on the model.It shows the history of the reaction, H(2S) + H2(lZ) (ortho) -+ H2(lZ) (para) + H(2S). . ( I ) The reader is referred to the above paper or to the book Atomic Reactions by Polanyi for a full discussion of this process. The second model is an enlargement of a small part of Model I. and shows the saddle region when the coulomb as well as the resonance forces have been taken into consideration. The contour lines were taken from the same paper by Eyring and Polanyi. The characteristics of the H, molecule are well shown. For example its heat of formation is negative to the extent of 18.8 Cals. and its energy of activation in decomposi-tion is 1.7 Cals. It is still unstable therefore even a t very low tem-peratures. The model also demonstrates the impossibility of its bi-molecular formation.A very similar model could be made to illustrate the C18 m~lecule.~ This molecule would probably have a slightly greater stability owing to the greater coulomb forces between the heavier atoms. Systems without Potential Barriers. There is a second class of triatomic systems differing from the first in that a stable triatomic molecule can be formed. In this class are the H-0-H H-N-H Cl-Hg-C1 and probably the 0-0-0 ti systems. A solid model of the potential energy curves could be made by fixing the angle between the three atoms a t the value for the triatomic molecule and plotting-as above. For all these systems a symmetrical model con-taining a deep valley would be obtained. There would be no repulsive forces except at small atomic separations and therefore no potential barrier would hinder the approach of an atom to the free radical.An interchange of atoms would invariably take place at a collision and as is well known the bimolecular formation of the triatomic molecule would be impossible. Nearly all reactions between true free radicals and atoms are of this type, The System of One Carbon and two Oxygen Atoms. Plate 111. and Fig. I show the system of one carbon and two oxygen atoms the three atoms being in a straight line as before with the carbon atom in between. Any divergence from a straight line requires an in-crease in potential energy. The carbon atom is a t the zero of spatial dimensions and the horizontal axes represent the distances of the oxygen atoms from the zero.The first is that of a 8P carbon atom and two sP oxygen atoms in which the oxygen This model is a composite model of two separate systems. 4 Rollefson and Eyring J . A .C.S. 54 170 1932. 6 It is not certain as yet whether the normal Oa molecule is in a singlet or a triplet state. See however Lain& Compt. rend. 196 910 1933 C. F. GOODEVE 63 atoms compete for the carbon atom to form a lZ carbon monoxide molecule. The potential energy curve of this system will be of the first type (H-H-H) and a collision between an oxygen atom and a carbon monoxide molecule will result in an interchange of atoms provided the high energy barrier can be overcome. The other system is that of a 5S carbon atom6 and two 3P oxygen atoms and belongs to the second class of triatomic systems.The four electrons of the carbon atom are in a " q '' state giving the atom four valencies with which i t attracts both oxygen atoms to form a lZ 360 carbon dioxide molecule. The poten- 300 tial energy at any point as shown on 240 the model is that of the system which has the lower value a t this point. iau The values have been obtained by an I20 60 application of Morse's equation to the known constants of the molecules,s~g but are not to be considered as in any way exact. The true curve FIG. 2.-A cross-section along cannot however be very different from that shown. These two systems can be made more clear by reference to Fig. 2, which shows a cross-section of the model along the dotted line " aa," (Fig. I ) .By taking this cross-section the distance of one oxygen atom from the carbon atom is fixed and the curves give the variation in the potential energy as the other atom is moved. Curve 11. is that of the normal lZ carbon dioxide molecule which on being broken up yields a 317 CO molecule 10 and a 3P 0-atom at a potential energy of 265 Cals. above that of the energy-less CO molecule. The 317 CO molecule has the nature of a free radical with two free valencies and is an activated molecule with 138 Cals. of energy above the normal lZ molecule. The interaction of the latter with an 0-atom ("p> is probably of the 3Z H, type as shown by Curve I. The exact shape of the curve is not known but it must be similar to that indicated. The two curves cross and a t u o " aa " (Fig.I). 6 See Pauling J.A.C.S. 53 1367 1931. 'I Hund 2. Physik 73 565 1932. 8 For CO see Jevons' Report on Band Spectra of Diatomic Molecules 1932. 1 0 There is some disagreement between the energy levels concerned and the I f the energy required to dissociate the carbon For CO see Martin and Barker Physic. Rev. 41 291 1932. values of the heats of dissociation. dioxide molecule is calculated by summing as follows : CO,(lZ) -+ CO(311) + O(3P) . . . . . 3. 265 Cals. (A). and then by a second method, CO2(1ZI) -+ CO(12) + O(sP) . . . . . + 127 Cals. CO(1C) 3 C(3P) + O(aP) . . . . . + 230 ,, C(3P) 3 C(6S) . . . . . . . . . . . + 37 ,, CO,(12) + C(sS) + O(3P) + O(3P) + 394 Cals. two values differing by 37 Cals. are obtained. Either the data for the 3 l 7 level are incorrect or a new sI7 level must exist.Adel and Dennison (Physic. Rev., 44 gg 1933) have recently calculated the potential energy function for CO, in the form of a Morse equation and give a different value for equation A. These disagreements affect only the curves in Fig. 2 64 THREE DIMENSIONAL MODELS the point of intersection there is the possibility of an adiabatic elec-tronic change (predissociation) taking place. Thus the whole of 265 Cals. may not be necessary to dissociate the carbon dioxide molecule nor need a CO molecule continue to repel an O-atom a t short distances. Between the two states there is a potential energy barrier similar to but not necessarily identical with an energy of activation. I t is extremely likely that the probability of the system passing over the barrier will be a function of the total energy (temperature) of the system but until this function is known no definite relation to an energy of activation can be made.O-atoms and ‘27 CO molecules can now be traced. For every such collision there will be a probability of the system passing over by an adiabatic electronic change into the carbon dioxide molecule. The molecule so formed would have a large amount of vibrational energy in one degree of freedom (in the linear system) and there is the same probability of the reverse electron change a t each half vibration. This “ activated ” COz molecule will have an appreciable life and may be deactivated by a collision or by radiating energy resulting in a stable molecule. We thus have the possibility of the bimolecular formation of the CO molecule.I t follows that the reverse process the unimolecular decomposition of this molecule should also be possible. This has been pointed out by Mecke l1 and by Herzberg.12 Collisions with a high energy will have a high probability of formation and a high probability of decomposition of the CO molecule. The life of the latter will be short and triple collisions may be necessary to stabi-lise the molecule. High energy collisions will generally result in an interchange of the oxygen atoms the potential energy of the system following the dotted line in Fig. I . I t is to be noted that the bound oxygen atom becomes more closely bound on the approach of a second oxygen atom but is finally repelled out of the system.A similar result will arise from collisions in which the atoms are not in a straight line. The potential barrier to be overcome in such cases is higher and the probability of a collision of a certain energy being effective is less than in the linear system. A carbon dioxide molecule if formed would be vibrating in its two unsymmetrical modes with high energy, but owing to the coupling of these modes by the rotational energy i t may dissociate in a short period of time by way of the lowest point of the barrier that is in a straight line. Effective collisions in non-linear systems may therefore need triple collisions to stabilise the molecule. The model which is typical of all linear triatomic molecules can be used to demonstrate the modes of vibration of the molecule.Such mole-cules have one symmetrical and two unsymmetrical modes as follows :-The history of collisions between o c o o c o t o J C .To-t + 3-++ ’The symmetrical mode is shown by a cross-section of the model along the line “ bb,” Fig. I and the first unsymmetrical by a cross-section along “ cc.” The third cannot be shown on this model but could be shown on a different type of model in which the symmetrical vibration was “frozen,” thus fixing the distance between the two oxygen atoms. I t will be observed that the line “ cc ” is a t right angles to “ bb.” This l1 2. physical. Chew. 18B $53 1932. la Ibid. 17B 68 1932 C. F. GOODEVE 65 follows from the fact that for small amplitudes of the first unsymmetrical vibration the distance between the two oxygen atoms is a constant.The potential energy curves for the system N-N-0 are very similar to those for 0-C-0. The curves will be unsymmetrical. The System of Two Sodium and One Chlorine Atoms. Interesting conclusions can be drawn from the interpretation of the chemiluminescence observed in the reaction between sodium vapour and chlorine on the basis of the potential energy curves. Polanyi and co-workers13 have shown that the energy is derived from the reaction, Cl(32P) + Na,(lZ) -+ NaCI(lZ)* + Na(32S) + 77 Cals. . ( 2 ) Their experimental evidence led to the conclusion that most of this energy appears as vibrational energy of the NaCl molecule. On a subsequent collision of this molecule with an Na atom the latter is activated and emits radiation thus, NaCl(lZ)* + Na(32S) 3 NaCl(lZ) + Na(32P) .(3) - (4) Na(32P) -+ Na(32S) + hv (D-line) . Their results indicated that nearly 100 per cent. of the collisions of re-action (2) result in the emission of radiation. FIG. 3.-The system of two sodium and one chlorine atoms with one sodium atom in between. Plate IV. and Fig. 3 show the potential energy of the above system. One of the sodium atoms is taken as the zero of the spatial dimensions l3 Beutler and Polyani 2. Physik 47 379 1928 ; 2. physikal. Chem. IB 3, 1928 ; Bogdandy and Polyani ibid. pp. ZI ; Polyani and Schay ibid. pp. 30. THREE DIMENSIONAL MODELS and the two horizontal axes represent the respective distances of the sodium and the chlorine atoms from the zero. In view of the lack of evidence as to which angle of approach represents a minimum of potential energy it is assumed that the three atoms are on a straight line.The potential energy contours shown on the central part of Fig. 3 have been obtained by a rough combination of the two curves shown on either side. The data for the Na molecule are from Jevon's Report 8 but no spectroscopic data for the NaCl molecule are known. The Na-Cl separa-tion in a crystal is 2.8 A.U. but it is probable that the separation in an isolated molecule is much smaller than this. The ratio of the separation in the crystal to that in the free molecule for both AgCl and AgBr is approximately 2 to I . The value 2'2 A.U. used in the diagram probably represents an upper limit. The heat of dissociation was calculated by Beutler and P01anyi.l~ The position of the point " b," the nearest dis-tance of approach of a sodium atom to a sodium chloride molecule without increase of potential energy is of importance to the following argument.This distance has been taken as 3-5 A.U. which is slightly less than the Na-Na distance (4.0 A.U.) in the crystal. A small coulomb force valley may exist in this region. This system has a spectroscopic similarity to the first system, (H-H-H) in so far as i t is made up of singlet states of the molecules and doublet states of the atoms. On the other hand it differs in the fact that the two stable states of the system are a t widely different energy levels instead of being a t the same level. The difference between these energy levels is the heat evolved in reaction (2).The diagram shows that the energy of activation which normally accompanies reactions of this spectroscopic type is absent in this case the potential energy barrier having been lowered by the strong attraction of the chlorine atom for the sodium atom. This is in agreement with the observations of Polanyi and co-workers who found that every collision between a sodium molecule and a chlorine atom was effective. The history of a collision is shown by the dotted line Fig. 3. A chlorine atom on approaching attracts the nearer sodium atom and repels the other but the repulsive force is very weak compared with the attrac-tive force. The result is that the first sodium atom is drawn violently to the chlorine atom leaving the other atom almost a t a standstill.Most of the heat of the reaction appears as vibrational energy in the sodium chloride molecule in agreement with the conclusions of Polanyi and Bray. The same will be true to a greater or less extent in all highly exothermic reactions such as for example the reaction, H(2S) + Cl,(lZ) 3 HCl(lC) + Cl(,P) + 44 Cals. - ( 5 ) where the normal atomic separations of the Cl and the HC1 molecules are 1-98 and 1-27 A.U. respectively. To complete the phenomenon of chemiluminescence according to Polanyi's mechanism a second collision is necessary the highly vibrating molecule colliding with a sodium atom ( 3 2 S ) and raising it to the neigh-bouring 32P level (reaction 3 ) . Such a process is merely the retracement of the dotted line in Fig. 3 up to say the point " a " where an electronic change takes place resulting in a 3 2 P Na atom and a lZNaC1 molecule containing less vibrational energy.The height of this resultant state on the potential energy scale is shown by the broken curve in the right hand part of the figure. The broken curve is a cross-section of a second three dimensional curve in which one of the sodium atoms is in a s2 C. F. GOODEVE 67 level.14 This second curve lies above the first and in no place does it inter-sect it. The electronic change is therefore not of the adiabatic (pre-dissociation) type but is probably due to resonance coupling between the vibrating NaCl molecule and the electron of the Na atom. According to the Franck-Condon principle this change can only take place with a minimum change of the atomic separations and will therefore take place a t a position of low potential energy and high kinetic energy such as the point " a." The phenomenon is completed by the change of the Na atom from the 32P level to the 32S level with the emission of the D line.If it is assumed that the system having arrived a t the point " a " can change over by an electronic change as described then any system of two sodium and one chlorine atoms which finds itself a t this point should be able to undergo the same change irrespective of the previous history of the system. A system starting from the left in Fig. 3 on reaching the point " a," should be able to change over to the state containing an activated Na atom and the reaction, At this stage difficulties in the above mechanism arise.Na2('Z) + C1(32P) -+ NaCl(lZ) + Na(32P) + 29 Cals. . (6) should take place. This reaction is excluded in the Polanyi mechanism, but as is seen the latter requires the difficult assumption that the sodium atom of the second collision is different in some way from that produced in reaction (2). My thanks are due to Mr. D. H. Lamb for his assistance in the making of these models. (Added in Proof) .- A possible solution of these difficulties arises from a consideration of the effect of varying the angle between the atoms. There seems little doubt but that the potential energy curves of the two systems Na(2S) + Na(2S) + C1(2P) and Na(2S) + Na(2P) + C1(2P) do not intersect one another nor approach one another a t any point so long as the atoms are considered as in a straight line.Alteration of this condition might lead to other conclusions but the possibility cannot as yet be profitably discussed. The fact remains that chemical energy is converted into electronic energy ; thus if the principle of conservation of momentum and the Frank-Condon principle are both to hold a t the moment of conversion the potential energy curves must cross or approach one another very closely for some spatial arrangement of the atoms. The Polanyi mechanism might be possible if the following considera-tions were valid. The second sodium atom (reaction 3) differs from the first sodium atom produced in reaction 2 in the fact that it may spend a longer time in the company of the vibrating NaCl molecule. If the electronic rearrangement requires a finite time (a not very likely supposi-tion) a second sodium atom would be treated preferentially to the first.Another perhaps more important difference betweeen the two Na atoms lies in the opportunity possessed by the second atom to attack the NaCl molecule along a straight line with the C1 atom in between. If the point of intersection of the potential energy curves occurs only a t such an angle the possibility of the one-stage process reaction 6 is not Part of this second curve is given by the cut-away part of the inserted section shown in the photograph THREE DIMENSIONAL MODELS large. Neither of course is the chance of attack of the second atom along such a line. Either one or the other of these possibilities might lead to a preference for the two-stage process rather than the one-stage, but neither excludes the latter.Even if there were no preference for a single collision there are many collisions of foreign sodium atoms reaction 3 which may lead to the bulk of the reaction following the Polanyi two-stage mechanism. Thus if the chance of the electronic rearrangement taking place is one in ten irrespective of the previous history of the three atoms and if the vibrating NaCl molecule is able to retain its energy through more than ten collisions, then one-tenth of the reaction will occur in one-stage while the remainder will go via the vibrating molecule. Polanyi and Schay found that the chemiluminescence of the sodium-chlorine reaction was much more readily quenched by added nitrogen than was the fluorescence of pure sodium vapour. This is the main experimental evidence in favour of the two-stage mechanism and involves the assumption that the vibrating NaCl molecule is deactivated by practically every collision with a nitrogen atom. I t is unlikely that such a molecule would be able t o retain its energy through ten collisions with sodium atoms as required in this third possible explanation. These considerations lead to the conclusion that the one-stage process is more likely to be the correct one but that the Polanyi mechanism is also possible. The Sir William Ram?ay Laboratories of Inorganic and Physical Chemistry, University College London

ISSN:0014-7672    

DOI:10.1039/TF9343000060

出版商:RSC    

年代:1934

数据来源: RSC