ION-MOLECULAR REACTIONS IN GASES

V. L. TALROSE Institut Khimicheskoy Fiziki, Moskva, S.S.S.R.

INTRODUCTION Over the last few years there has been an ever-increasing interest in gas phase reactions of ions with molecules. This problern is closely related to the chemistry of high energy reactions in which the primary acts are induced by imparting to rnolecules, quanta of energies rauging from unity to sorne several tens of electron-volts. Radiation chemistry, the chernistry of electric discharge reactions includ­ ing rather dense plasrna, the chemistry of high and ultra-high temperatures as well as photochemistry, are all components of the chemistry of high energy reactions, especially so when examined with respect to the elernentary steps involved. The question as to what is going to occur if an ion collides with a neutral particle is not new. I t arose from the first enquiry into the processes occurring in gas discharge tubes. It becarne evident soon enough that the operation of gas devices used in nuclear physics is closely related to collisions of this kind. One " physical " problern has had a completely " chernical " aspect for a considerable time. This is the problern of controlling the composition of ions from a hydrogen ion source; the reaction1

Ht + H 2 --+Ht + H (1)

is known to play an important part in the processes responsible for this reaction. This ion-rnolecular reaction attracted the attention of physicists some 25 years ago and proved to be the touchstone for the activated complex problem2• Naturally chernists have also been concerned for some time with the importance of gas phase ion reactions. The firstessential steps in this direc­ 3 tion were rnade in radiation chernistry and were due to Lind • The first experimental direct determination of ionic reactions in radiation chemistry was also carried out long ago. Two such methods will be mentioned here: that of measuring critical electron energies corresponding to the onset of chemical conversions in the system4 and the ion extraction method discussed in a nurober of Essex's works5• However, it is striking that although ionic reactions were studiedunder macroscopic conditions, at high pressures, systematic direct investigations of element~ry ion-molecular reactions were not undertaken either within 455 V. L. TALROSE the nineteen-twenties and -thirties, or in the -forties~ Yet the importance of such studies should have been evident from the experiments of Bonhoeffer and Harteck which were concerned with elementary radical reactions. This is the more puzzling since mass spectrometry was already in use at that time and physicists had, in fact, made the first observations on ion-molecular reactions ; these were reaction ( 1) and

(2) studied in 1940 by Tate et al6• (However, some confusion was introduced by the appearance potential of H 30+, which was erroneously determined as higher than the ionization potential ofwater.) The first attempts to apply mass spectrometric investigations to chemistry seem to have been made in 1936, by Eltenton and Vassiliev7•8 in Kon­ dratiev's laboratory at the Institute of Chemical Physics. These investigators attempted to find out what were the ionic processes occurring in electro­ synthesis of organic substances from CO and H 2, and of ammonia from N 2 and H 2• By gradually increasing the pressure in the mass spectrometer 1on soun~e and measuring the appearance potentials they obtained the reactions

Nt+ H 2 ~N 2 H+ + H (3) and CO++ H2~ COH+ + H (4)

But leaving history aside, let us consider the present state of affairs and the recent works. Systematic work in the given field has been carried out for about 10 years in a number of Iaboratories by scientists of many countries, chiefly by Stevenson, Field, Franklin and Lampe, and Hamill in U.S.A., by our Iabo:ratory in Moscow, by Lindholm in Sweden, by Henglein in Germany, by Cermac and Herman in Czechoslovakia, and by a nurober of other investigators. Finally, I should like to draw attention to the survey of works on ion-molecular reactions published recently by Stevensan and Schissler, in the chapter "Mass Spectrometry and Radiation Chemistry" of the collected works edited by Haissinsky9• I presume that my audience will agree that it would be more reasonable forme to deal in greater length with the work of our own laboratory, rather than to aim at a full survey of the available literature. In order to bring about a 1nore lively discussion I propose to dwell on problems which arenot yet completely elucidated.

1\IASS SPECTROMETRIC INVESTIGATIONS OF ION-MOLECULAR REACTIONS The methods for investigating ion-molecular reactions fall into two basic classes: the first involves the generation of primary ions by electron irradia­ tion, or sometimes by light, within the same chamber in which these ions collide with molecules. Weshall define it as internal ionization. The second 456 ION-MOLECULAR REACTIONS IN GASES dass involves ions obtained from an external source and introduced into the collision chamber as a separated or non-separated beam. Let us call this the external ionization method.

The internal ionization method A characteristic scheme of internal ionization is shown in Figure 1. An electron beam of pre-determined form is directed into the space between plates I and II, i.e. into the reaction zone. Some of the primary ions succeed in colliding with molecules in the space between plates I and II; the primary and secondary ions are repelled from the reaction zone by the electric field either arising from the potential difference between plates I and II, or from that between plates III and II. Upon passing through the exit slit of plate III the ions are markedly accelerated and then subjected to mass­ spectrometric analysis.

Plate I 0 0 0 0 00 0 <__;:f~+--4°:__--:o;+--run?f:--- _<~E,!ectron beam ions Molecule--0

0 Plate TI umuzm,m "'"

Platem )??ij22?222242P""' "

The primary task of the internal ionization method is the identification of the ion-molecular process as such. This problern is solved more-or-less similarly in all studies. The secondary nature of the ions and the neutral initial products are determined from the secondary and primary ion currents as a function of the partial pressure of the components of the mixture in the collision chamber. Primary ions taking part in the ion-molecular reaction are identified by the appearance potential of secondary ions. Thus, suffici­ ently accurate determination of ion potentials is of prime importance. The method for quasi-monokinetization developed by Fox10 has been developed in our laboratory11 to an automatic procedure by modulation ofthe electron­ retarding potential and resonance amplification of the ion current at the frequency of this modulation. Curves obtained in this way for the appearance ofprimary and secondary ions in various processes investigated by us are shown in Figure 2. It may be seen that H 30+ ions are actually obtained from H 20+, and the C 2H 50Ht ions via C 2H 50H+. In many cases, the high background of some primary ions with the same mass number hinders the detection of secondary ions. A high-resolution spectrometer is very desirable in this case. For instance, the CHt ion observed in our laboratory12 in the reaction

CHt + CH4 --7 CHt + CH3 (5) 457 V. L. TALROSE has the same mass number as the 13CHt and 160H+ ions, present in the vacuum background. To provide confirmation of the appearance of CHt, we used1a, in interpreting the multiplet associated with 17 atomic mass units (amu), a mass spectrometer of high resolution, designed by Alexeevskii at the Institute of Physical Problems in Moscow14. This multiplet obtained under conditions when traces of ammonia were introduced into the mass spectrometer besides methane and traces of water, can be seen in Figure 3.

4 ~ 4 ~ 80 ·c: PH o" 2xto- mmHg § Pc2HsoH=2x1o- m mHg I 2 C H 0W ~ 30 1---·+--+- 2 5 t------+----< _l. L.. -e 6 0 s ~ C2H50H2• c 20 t-----i--1-1-­ V a.. ~ 40 1-----+--H L.. H o• ~ ~ x7·5 ... 3 ·,~o-'· ::J ~ 10 u I ,.; c 2 0 t-----+---t-­ . c I 0 ~,· .2 • e''3C .! ~ ,,\so\~? • - 12 13 14· 15 .e!---1 L__~ 11 12 10 11 12 13 energy vorts Etectron energy votts Figure 2 (a). Ionization efficiency curves for Figure 2 (b). Ionization efficiency curves for

H 20+ and for secondary H 30+ ions C 2H 60H+andforsecondaryC2H 50H2 +ions

The above refers to methods for identification of ion-molecular reactions. The determination of rate constants will be considered separately. The current methods devised for this problern include one of continuous repulsion developed in the U.S.A. by Stevensan and co-workers15 - 17 and Field, Franklin and Lampe18 - 20, the pulse method devised in our labora­ tory21-24, and the increased-pressure method (Melton and co-workers25-27, Saporoshchenko28 and Field29).

~ V)100 :: ·'§ 80 B .a~ so § ~ ~0 ...... 20

17·008123 12·03188 117.04444 17·04000 Mass ...- Figure 3. A 17 amu multiplet, the resolution of which demonstrates the CHt ion appearance

The method of continuous repulsion-This method is widely used because of its relative sim.plicity. A fixed potential difference is maintained between plates I and li ~~Figure 1) during measurements. The pressures in the collision chamber are I0-5 to I0-3 mm Hg, and only a fraction, I0-1 to I0-3, of all ions has a chance of colliding with a gas molecule before leaving the chamber. 458 ION-MOLECULAR REACTIONS IN GASES The main problern in this case will be the determination of the relation between the phenomenological cross-section Q in equation

(i) where / 2 is the current of secondary ions, / 1 that of primary ions, N the concentration of molecules taking part in the secondary process, and L the primary ion path in the collision chamber, and the reaction rate constant k, corresponding tothermal equilibrium in ion and molecular reaction rates. This is usually of interest to chemists. Q will naturally depend on Land the field intensity in chamber E, and it appears that the derivation of a sub­ stantiated theoretical equation for calculating k (and the true microscopic cross-section a) from the Q value obtained is often a complicated and a far-from-solved problem. Thus, it would be natural to approach the determ­ ination of k under conditions when ions and molecules are in thermal equi­ librium. The pulse method-The pulse method permits, in principle, the realization of the above conditions. The electric beam is switched on as a pulse for a very short time tb shorter than that ofthe thermal motion ofthe ion through the collision chamber. After this, there is a delay td during which equi­ potential conditions are maintained in the chamber (as in the t1 period). The potential difference is then supplied in pulses (tr) repelling the ions. Under conditions of uniform ionization and similar repulsion for all points of the ionization zone, the It,/11 ratio of ion currents formed by reaction A+ + B----+ C+ + D (6) will be

(ii)

where Nis the concentration ofB, m1 the mass of A+, m2 the mass ofC+, and

ß = yB11:kT (iii) d here d is the distance from the site of ion appearance to the ionization chamber wall. and (iv) we obtain (v)

459 V. L. TALROSE

where F(ti,tr) is a certain function of the ionization time ti and repelling time tr. By varying the delay time td and measuring I"t:)It._ as a function of td, it is possible to find k, if N is known. Equation (v) holds for td values correspond­ ing to conditions when ions do not succeed in reaching the wall or leaving the chamber. Thus the method is quite similar to usual kinetic investigations: the degree of conversion is determined as a function of time elapsed from the onset of the reaction. Whereas routine kinetics deal with hours, minutes and seconds, in the case given, td = 3 to 20 microseconds. More explicit analysis shows that for m1 ~ m2 equation (v) will be valid also when con­ dition

is unfulfil.led, and, in this case, the method appears to be especially con­ venient. The ohserved linear dependence of IcHtflcHt on td for the reaction

(5) is shown in Figure 4. The linear dependence is evident and, consequently,

k = tan r:1. (vi) N where r:t., is the slope of the straight line.

;! 18 16 1/.v 14 •;t12 I /. ~10 )/ / r--l7 ~ tan9 a.=Nk ~

0 2 4 6 8 React ion time !J. sec

Figure 4. The IcHt /IcHt ratio as a function of the reaction time when using the pulse method

Another possibility given by the pulse method is that of considerably increasing the 13/It.. ratio by taking a sufficiently high td value and mc > mA. This has recently been clone in our laboratory24• High 1{:)11 ratios would be 460 ION-MOLECULAR REACTIONS IN GASES important in the identification of any secondary process, especially when the secondary ion is identical to one of the primary ions present in the chamber. This condition will always arise in investigations of charge exchange processes by the internal ionization method. For instance, in studying the reaction Xe++ CH 4 ~Xe + CHt (7) secondary ions would have to be detected on a strong background of primary CHt. By using the pulse method, we succeeded in increasing the CHt (sec)/ CHt (prim) ratio by two orders, as compared with the ratio obtained by the method of continuous repulsion. The increased-pressure method-By increasing the pressure in the ionization chamber up to about 10-1 to 5 X 10-1 mm Hg, it becomes possible to observe, along with secondary processes, "tertiary" and higher processes, i.e. to obtain conditions approaching those for real systems. The basic methodological improvement consists of using more powerful pumping systems and increasing the degree of differential pumping for the source and analyser regions. Both cx-particles and ordinary electrons of several tens eV were used for ionization. The repelling field seemed to be the same as in the continuous repulsion method. Since even at the highest 29 30 pressures (0·3 to 0·5 mm Hg • ) used, a certain fraction of the primary ions still leaves the chamber without colliding, it may be inferred that the experimental conditions reported are far from those required forthermal equilibrium between ions and molecules. Simultaneaus application of the high-pressure method and of some variant of the pulse method would probably prove to be of great interest.

The external ionization method The external ionization method has already been used by physicists for investigating collisions between fast ions and atoms and, in some cases, 31 34 35 simple molecules - • Lindholm - 37 was the first to apply it funda­ mentally when studying collisions between ions and multi-atomic molecules; 42 it has also been used in our laboratory in recent years38- (Figure 5). Two

Plate f 0 0 0 o · Ion T"' T < beam 0 ~s o-....._.,~econdary .10n 0 0 o. o._:::_'::::->.Molecutes Plafell iuuuu?lc!Wc?l "V22ä?c?r?c u?cü?U

p (a fe Jll !Zz:lu:222c<

Mass separator Figure 5. Diagram of the external ionization method features of this method will be noted. As the secondary ions were always repelled normally to the primary ion beam, the recorded portion of the secondary ions that have obtained kinetic energy was always lower than that of the slow secondary ions. This permits a distinction between 461 V. L. TALROSE resonance and non-resonance processest. However, it will be bornein mind that a certain small portion of the secondary ions possessing super-thermal kinetic, energy Ek will nevertheless be repelled, and special experiments or, at least, calculations of the effective repulsion for ions of various Ek values would be of value. The second feature of the external ionization method is the difficulty encountered in passing to relatively slow primary ions. This is the necessity of ensuring an adequate geometry of the beam of slow ions. Moreover, this bea1n should not contain electrons abstracted from the edges of electrodes in the ion retarding system. In practice this method is good for ions retarded to 30-10 eV only.

RESULTS OF MASS SPECTROMETRIC INVESTIGATIONS ON ELEMENTARY ION-MOLECULAR REACTIONS

Classifi~cation of reactions In classifying ion-molecular reactions by the results obtained, and not by the reaction mechanism, these reactions would fall into two types: ( 1) transfer and rearrangement of heavy particles, and (2) charge exchange (i.e. electron transfer) with or without dissociation. The observed and more-or-less studied reactions of type 1 are summarized m Table 1, and those of type 2 in Table 2.

Table 1. Transfer of heavy particles and/or rearrangement

Class of reactions Investigators Examples Positive ion-molecular reactions H atom transfer 7 RH+ rvi+-+R + MH+ Eltenton Nt + H 2 -+ N 2H + -f H Proton tra:nsfer Talrose { 43 RH+ + M-+ MH+ + R Frankevieh Ht + H 20-+H30+ + H "Combined" transfer 1 RH++ RH-+RHt + R Smyth H:t + H 2 -+Ht + H H- transfer fField C 3Ht + n-C5H 12 -+ n-C~>Ht 44 Rt + R 2H-+R1H + Rt Lampe + CaHs Transfer of heavy atoms Pottie { 45 M+ + XY-+ MX++ Y Barker I++ CH3I-+CH3 + I:t Transfer of heavy ions Pottie 45 M + XY+-+MX+ + Y Barker HI+ + CH3 -+ CH3It + H " Combined " transfer of heavy Hogness { 46 atoms Harkness I:t + I 2 -+ It +I X;t + Xz -+ Xit + X Rearrangemen t fStevenson AB++ CD-+AC+ + BD Schissler15 Association Pottie { 47 M+ + 1\1-+Mt Hamill 2C3H 7I+-+ (C3H 7I):t Negative ion-molecular reactions Neutraltransfer 48 A-+XY-+AY-+X Muschlitz H- + H 20-+0H- + H 2 Rearrangement Henglein { 49 Muccini o- + CH3N0z-+ CH2NO; + OH

t Strictly speaking, secondary ions will obtain a certain kinetic energy as a result of the resonance process as well, since an appreciable " impelling " interaction between the ion and induced dipole occurs at very high impact parameters. 462 ION-MOLECULAR REACTIONS IN GASES Table 2. Charge exchange reactions

Class qf reactions lnvestigators ~ Example .------Positive ions Resonance charge exchange ·{Klemann without fragmentation Rosenao A + + XY-+ A + XY+ ~Evlr ~ 0 3 Resonance charge exchange Lindholm a N+ + CH4 -+N + CHt + H with fragmentation A + + XY -+ A + X+ + Y !~.Ever ~ 0 Non-resonance charge ex­ Lindholm35 change without fragmentation A + + XY-+ A + XY+ !l.Ever ~ 0 Non-resonance charge ex­ !Lavrovskaya change with fragmentation ~ Markin A + + XY-+ A + X+ + X l Talrosen !l.Ever < 0 Negative ions Resonance charge exchange Dukelskii without fragmentation { Zandberg62 A- + XY-+ A + XY­ (Nature of transfer undeter­ JHenglein mined) l_Muccini49

t" Vertical " heat of reaction.

Constants and temperature dependences The cross-sections cr of known processes are within the range of I0-13 to I0-18 cm2, and rate constants for temperatures of 400 to 500°K within I0-9 to I0-13 cm3 jmolecule sec. Consequently, the upper limits of observed cr and k values are about 1-2 orders higher than the usual gas-kinetic values. I t will be noted that this holds both for type 1 and type 2 processes. Lower Iimits depend upon the apparatus used; for a number of reasons, slow pro­ cesses are more difficult to observe by the mass spectrometric method. Information on the temperature dependence of k is still scanty and refers to type 1 processes. Stevensan and Schissler16 found that no temperature dependence of the rate of transfer of hydrogen atoms from hydrogen molecules to simple ions. On the other hand, the same investigators15 and Frankevieh with the author53 found that there is a slight decrease in a with temperature, similar to the 1 I~ T function which is found for certain other reactions of hydrogen transfer. Along with a great number of observed processes characterized by high k values, these data provide confirmation of the fact that ion-molecular reactions, at least atom- and hydrogen-ion transfer, proceed without true activation energy. Whether this holds for other non-resonance ion-molecular processes, is not quite clear. There seems tobe only one example (obtained from sturlies other than mass spectrometry) of an ion-molecular reaction having a true 463 P.A.C. (VOL. 5. NOS. 3-4)----,11 V. L. TALROSE activation energy ( "'7 kcaljmole). (It was investigated by Pshezhetzky and 54 Dmi triev .)

Nt+ 0 2 ------7>-NO+ +NO (8) This reaction is seen to be one of rearrangement. At the same time, the rearrangement reaction investigated by Stevensou and Schissler15

(9) proceeds without appreciable activation energy. Energy transfer To understand the mechanism of ion-molecular processes, as well as any other elementary act, it would be necessary to obtain data on the importance and various conversions of energy occurring in this process.

1·8 ~ l6 "§ 1-4 .ri ::,0 l2 c: ~ 0·8 ao-e- 0 ...... § 0·4 + -•-•-CH3 0-2 -· 0 10 20 30 40 50 Xenon pressure (arb.units) Figure 6. The currents of CHt and CHt ions formed in a methane-xenon mixture as a function of Xe pressure

The ~ffect of excitation energy-This effect wa~ studied by Czechoslovakian scientists55 for the transfer of heavy atoms; they made use of electron excitation reactions only. lt appeared that the reactions observed:

Nt+N2 -----7>-Nt+N (10) o; + 02-----3>-o::- + o (11)

2 involve electron excited ions Ni(B ~t (and Ot(2II 4). The phenomenological yield of secondary ions in these processes at pressures in the collision chamber amounting to l 0-5-1 o-4 mm Hg appears to be several orders lower than with non-excited particles, as the majority of excited ions succeeds in emitting light before colliding with the molecule. This is apparently the reason why there is no information on the part played by excitation in reactions involving ions participating simultaneously in secondary processes in a non-excited state. The secondary reactions involving non-excited ions would mask the reactions of the few ions left excited at the time of collision. The effect of electron-excitation energy on processes of ion-molecular resonance charge exchange was studied very explicitly by Lindholm, who 464 ION-MOLECULAR REACTIONS IN GASES

35 37 used the method of external ionization - • His basic conclusion was that to obtain the ionizing vertical transfer, the molecule would require the sum of the ionization energy and the energy of electron excitation of an incident ion. The molecular ion formed will decompose (or not) depending upon its structure and the excitation imparted to it. For examp1e

2 Kr+( Pt) + H 2S-----+ S+ + H 2 + Kr ( 12) 2 Kr+( Pt) + H 20 --+ H 20+ + Kr ( 13) The part played in charge exchange by slow excited ions was studied 56 using the internal ionization method (Hamill and co-workers ), the increased­ 30 24 pressure method (Melton ) and, lately, the pulse method (our laboratory ).

0 C2H: xe· +C H ..--..5 2 4

$ 0 '§ 5 \:Sv, ..ci -\-

~4 0 X CzH2 c 30 ,_~ X Ö2 =---·-.-C2H;

c X ..91 "

0 10 20 30 40 50 60 Xenon pressure (arb. units)

Figure 7. The currents of C2Ht, C2Ht and C 2Ht ions formed in an ethylene-xenon mixture as a function of Xe pressure Charge exchange involving the excited Kr+(2Pt) ion

Kr++ CH4 --+Kr + CHt + H (14) was observed by the latter method. The excited state of the Kr+(2Pt) ion is "" 0·6 eV above the ground state and sufficient to make the reaction (14) exotherrnie by 0·2 eV. Fox et al. 57 showed that excited ions Kr+(2Pt) and Xe+(2 Pt) are formed in appreciable amounts in the ionization of Kr and Xe by electron impact. The excitation energy for the Xe+(2Pt) ion is 1·34 eV. This energy appears tobe sufficient for making the processes

Xe+ + CH4 --+ Xe + CHt (15)

Xe+ + C2H 4 --+ Xe + C 2Ht + H 2 (16) by 0·44 and 0·04 eV exotherrnie respectively. Meisels58 based his suggestion about the probability of process (15) on results of experiments concerned with radio1ysis ofmethane sensitized with xenon. We have, indeed, observed processes ( 15) and ( 16) by means of the pulse ionization method. The depend­ ence of secondary ion currents on the pressure of inert gas is shown in Figur es 6 and 7t. t All current values are given with respect to the Ne+ current; small amounts ofNe were added as standard. 465 V. L. TALROSE

Transfer ~f translational energy-Certa.in data on interconversion of the energy of translational motion of an ion and a molecule, and the internal energy in the course of the reaction, arealready available. There is little information, however, on reactions involving transfer of heavy particles. Frankevieh and the author41 found that an increase up to 15 e V in the kinetic energy of C 2Ht ions does not result in reaction (17) which is only 0·9 e V endothermic taking place. On the other hand, Herzberg and co-workers59 have recently observed an endothermic process

Hi + He-~HeH+ + H (18) and suggested that it may proceed at the expense of the translational energy. It will be noted below that certain results for polyatomic systems obtained by the continuous repulsion method may also be treated as due to transfer of translational into excitational energy. With charge exchange processes the conversion of kinetic to internal energy and vice versa for vertical transitions is known to be greatly hindered. Appreciable cross-sections for non-resonance processes would appear only at relative motion energies corresponding to the Massey criterion

ajßEI --""'hv - 1 (vii) where a is the cross diameter of colliding particles, Eis a resonance defect, v is the rate of relative motion of particles. On the other hand, it was noted many years ago60•61 that when the potential curves for initial and final systems intersect, the cross-section for a corresponding electron process may be considerable; an appreciable activation energy may be observed in this case, but the process may proceed also at lower rates of particles. For instance, Rasted and co-workers62 found that in the low-energy range the cross-sections for charge exchange processes A+ + Kr, Ne+ + A, c+ +Kr are many times higher than.would be expected from the criterion of (8). Similar results were obtained by Bydin and Bukhteev63 for the ionization of fast atoms of alkalimetals in collisions with H 2, D 2, N 2 and 0 2• Examples of considerable deviation from the Massey criterion were already known for atomic systems. Finally Magee64 suggests that when the particles are not too fast, charge exchange 1may occur via an intermediate complex of a lifetime exceeding one vibrational period. · The reaction would then proceed in the same way, as in heavy particle transfer, and the conversion of rotational to internal energy would seem to be markedly favoured. It should be stated at once that the available experimental data, those obtained both by Lindholm and in our laboratory, are not yet adequate for settling this problem. The main reason for this seems to lie in the fact that the geometry used involves a secondary beam normal to the primary one. This geometry permits good recording of very slow secondary ions 466 ION-MOLECULAR REACTIONS IN GASES only. Whereas when a second ion appears by a non-resonance reaction_ of a very fast primary ion with a thermal molecule, as is the case in using the external ionization method, the translational energy of the majority of secondary ions will be considerable and the portion repelled ( 17) small. In our device, for example, when an ion and a molecule of identical masses collide at an energy of 300 eV to form identical-mass particles via an inter­ mediate complex, '17 will amount to 5 per cent of the repelled thermal ions. As a result, resonance processes may be observed bu t non-resonance processes appear to be considerably masked. However, the '17 value appears to be sufficiently high for identification of certain non-resonance processes, both by Lindholm's and our apparatus.

0 • ~

0

0

~ clll ~c c Q.J t: • :::::1 u • ~CHi c .Q 4 Q.J . . > ./·:: ~

& •• (•• l I I I J 0 50 100 150 200 250 300 Energy of Xe+ vo l t s

Figure 8. The intensity distribution in the mass spectrum of Xe+-C2H 4 charge exchange products as a function of the kinetic energy of Xe+ ions

For instance, along with ion-molecular charge exchange, independent of the translational energy of the particles and their consequent resonant properties, it is sometimes possible to record inverse cases. The dependence of the spectrum for products of charge exchange Xe+ + C 2H 4 upon the kinetic energy ofXe+ (obtained in our laboratory) is given as an65·51 example in Figure 8. It may be seen that for sufficiently endothermic processes, such as + (7·14 eV (2P~) Xe++ 2 4 - (19) C H ---*Xe+ CH2 + CH2 6.8 eV (2P;t) there is an energy threshold, practically similar to that calculated from energy and momentum conservation, and the excitation function of this process shows an increase immediately after the threshold, considerably more steep than that implied by the quasi-adiabatic Massey hypothesis. On the other band, it would be of interest to consider an example of the pulse method application to this problem. It was shown66 that the spectrum for charge exchange between argon and methane, and between krypton 467 V. L. TALROSE and ethylene does not change in passing from the method of external ioniz­ ation by ions of 300 eV to the pulse method of internal ionization,, i.e. to thermal ions. Corresponding mass spectra of charge exchange products are shown in Table 3. Consequently, for a very broad range of energies, we seem to be concerned in this case with a resonance mechanism only.

Table 3. Charge exchange reaction products for fast and thermal primary ions

~' [.ons ~nergy Thermal 300 eV

Ar++ CH4 CHt 0·02 CHt 0·83 0·82 CHt 0•17 0·16

Kr++ C 2H 4 C2Ht 0·03 C 2Ht 0·60 0·60 C 2Ht 0·40 0·37 C 2H+ 0·002

The mechanism and theory of ion-molecular processes Let us now try to conceive the mechanism of chemical conversions that may take place in collisions of ions with molecules51 (Figure 9). Processes necessitating relatively high energies (impact ionization, dissociation, etc.) will be disregarded throughout this paper.

F(gure 9. Scheme of reaction mechanisms occurring in collision between Aß+ ion and CD molecule;

First of all it is necessary to distinguish between two mechanisms: the resonance (" long-range ") mechanism and that involving the formation of an intermediate complex. Of prin1e importance is the fact that the first mechanism will result in charge exchange only (or perhaps in resonance excitation transfer), while the second may involve the transfer of heavy particles as well. The pre­ dominant mode of the intermediate complex decomposition will be determ­ ined by its structure and excitation level. There is every reason to believe that 468 ION-MOLECULAR REACTIONS IN GASES qualitatively this scheme is true. Indeed, the resonance mechanism has been repeatedly observed in very different systems. Direct experimental sturlies of the mechanism involving an intermediate complex have been less explicit. However, a number of direct experiments providing evidence for the form­ ation of such complexes may be cited. For saturated molecules with a relatively small number of atoms such evidence was obtained in the experi­ ments of Frankevieh and the author53,67 which were concerned with the distribution of ions with respect to translational energies in reactions

Ht + H 2 --+Ht + H (1)

NHt + NH3 --+ NHt + NH2 (20)

H 20+ + H 20 --+ H 30+ + HO (2)

CHt + CH4 --+ CHt + CH3 (5)

It appeared that this distributionwas near tothat expected on the assumption that energy distribution is uniform over all degrees of freedom for the final products. Hamill and Pottie47 succeeded in detecting the complex ions formed in a reaction involving multi-atomic particles

(21) and which involved a lifetime of "' 10-6 sec. Using the pressure increase method, Field29 detected the complexes

C 2Ht + C 2H 4 --+ C 4Ht (22)

C 2Ht + C 2H 4 --+ C 4Ht (23)

C 2Ht + C 2H 4 --+ C 4Ht (24) and found their half-lives to be (0·2 to I) X 1 Q-7 sec. Thus, the ion-molecular problern should be concerned with at least two problems. Firstly, it is necessary to know the method of calculating cross­ sections for the resonance process and for the complex formation. Most important, at the given stage, seems to be the determination of their ratio and its dependence on the rate of relative motion of the particles. Secondly, a theory for calculating absolute and relative rates of decomposition of the intermediate complexes by various modes is necessary. How does the question stand with respect to the first problern? There exists a theory of resonance charge exchange. It gives a relation for the cross-section68

00

a = 2tr f P(R0 ) R0d R0 (viii) 0

2 where P(ilo) ~ sin [ ;v F(ilo)]

469 V. L. TALROSE

R0 is the impact parameter, and v the relative motion rate. However, this theory does not account for the possible formation of a complex. On the other hand, the existing theory of complex formation17 which is concerned, with certain restrictions, with non-polar moleculest does not account for possible resonance charge exchange. According to Stevensan and Gioumousis17 this theory, based on the classical work of Langevin69 gives an expression for a

(ix) where a is the polarizability of the neutral particle, f.L is the reduced mass, v is the rate ofrelative motion of an ion and a molecule. The rate constant of an ion_:_molecular reaction calculated by the activated complex method2

(x)

(kr is the theoretical k value, K the transmission coefficient of the transient state theory) may in a certain sense be considered as the rate of an inter­ mediate complex formation. A similar relation may be obtained without using the transition state theory. K will then have the significance of a collision " efficiency " co­ efficient only9•17• Gorrelation of the solution for the continuous repulsion method (obtained from Boltzmann's equation) with relations (10), (9) and (1), taken from the work ofreference 17, gives an expression permitting the determination of K from known values of Q, E and l, i.e.

(xi)

The first condition for the validity of this calculation is the proportionality 1/ l . of the 12/11 ratio to the r E value, or, what amounts to the same thmg, the inverse proportionality of Q to ,JEl. Indeed, this relationwas obtained by Gutbier7° and Stevensou and Schissler16 for a number of reactions between simple ions and molecular hydrogen. Moreover, in some cases K appeared tobe close to unity. On the other hand, as shown by Stevensan and Schissler and, particularly, by Field, Franklin and Lampe,20 the dependence of

I 2 / I 1 upon E appears to be more pronounced in more complex systems, i.e. it lies somewhere between 1/,JE and ljE. Field, Franklin and Lampe succeeded in deriving an equation for this dependence

_ 6007TK,JrxkT 1/m mN • I 2 1 + h (__!!!!__)t (xii) Jl - N E r mN arc sm 150kT where mN is the neutral particle mass, and k is the Boltzmann constant. t Hamill gave at the Congress an example of such a theory for polar molecules. 470 ION-MOLECULAR REACTIONS IN GASES Field, Franklin and Lampe also use equation (xii) for determining the K value, and for the cases they investigated it appears to lie between 0·5 and 1. It will be noted, however, that this equation was obtained as a result of a somewhat rash replacement of one of the three translational par­ tition functions in the initial equation of Eyring et al. 2 by the effective tempera ture 1 1 e2E 2t 2 -k8 = -kT + -- (xiii) 2 2 2m

Why the theory of Stevensan and Gioumousis should be used for simpler systems, and that of Field, Franklin and Lampe for more complex cases, is not clear. Though there is a large gap between the resonance charge exchange theory and that for the complex formation, attempts should be made to determine how these processes compete. This should be clone by comparing experimental results for various processes. For instance, Field, Franklin and Lampe noted that the rate constant decreases in the order

CDt + CH4 ----* CD4H+ + CH3 (25)

CDt + C 2H 6 ~ CD4H+ + C 2H 5 (26)

CDt + C 3H 8 --* CD 4H+ + C 3H 7 (27)

CDt + iC4H 10 ----* CD 4H + + iC4H 9 (28) while the polarizability increases. Stevensan stated in a private communic­ ation that the reactions of type

Kr+ + H 2 ----* KrH+ + H (29) appear to take place, while the exotherrnie reaction

Kr+ Ht--+KrH+ + H (30) is not observed. lndeed, the competing röle of charge exchange may be supposed to be obvious in all these cases. However, a number of inverse cases may also be cited. Thus, charge exchange with thermal Ar ions

Ar++ H 2 --*Ar + Ht (31) was observed in our laboratory along with reaction

(32)

The pulse method66 was used and the cross-sections for these reactions were comparable. However, according to Stevenson and co-workers16•17, the rate constant of reaction (31) is high and corresponds to K = 1. The same seems to be true for reactions (5) and

H{ + H 2 --*Hi + H, (1) 471 V. L. TALROSE though charge exchange at thermal energies was not investigated here. On the other hand, the reaction rate

Kr+ + H 2 ---+ KrH+ + H (30)

6 17 is not high (K = 0·3)1 • though charge exchange between H 2 and Kr+ ( 2Pi), as well as Kr+ (2Pt), is very endothermic. In making these comparisons it should be bornein mind that in discussing the competition with resonance charge exchange we are referring to the intermediate complex formation step and, consequently, to the firstproblern of the ion-molecular theory. Whereas in discussing the competition with non~resonance charge exchange, we usually pass to the second step and, thus, to the second theoretical problem, namely the relative probability of various intermediate complex decomposition modes. What is the position with respect to the second problem, that of the decompo:;ition of complexes? Field, Franklin and Lampe20 suggested that it may be solved by means of the theory for the decomposition of excited ions, developed earlier by Eyring and co~workers 71 for dissociative ionization by electron impact, and based on the concept of random distribution of the excitation energy among all the vibrational and rotational degrees of freedom. A great similarity was observed, in particular, between the spectra of decomposition products in reactions (22), (23) and

(33) and those for the products of dissociative ionization of l~butene, 1 ,2~butadiene and vinylacetylene. It must be emphasized that the quasi~equilibrium theory should be used in this case no less cautiously than in the interpretation of mass-spectra involving large molecules, as the main postulate for energy distribution in an excited ion is far from being always fulfilled, as has been shown, for example, by Tunitzky72•73• However, for complexes that are not so large (and probably not too small), the use of this theory, at least for semi-quanti­ tative treatment, may prove justifiable (see also references 45 and 4 7). It will be noted that in investigating the complex decomposition by the continuous repulsion method, and especially by the external ionization method, no allowance was made for the considerable additional excitation of the cornplex by the imparted energy of the relative ion-molecule motions. The fact that this excitation may affect the decomposition mode seems to be obvious. Less exotherrnie modes, including that of inverse decomposition, will becmne more probable. When this is taken into account, our approxim­ ate equation of the secondary ions current takes the rather cumbersome form

(xiv) where S i.s the portion of kinetic energy converted into the internal energy of the cmnplex, E* is the energy released by complex formation, and Ei is the activation energy for decomposition of the complex by the i-th mode. 472 ION-MOLECULAR REACTIONS IN GASES This equation supports, in particular, a more marked dependence of

12 /11 on E, rather than on lf.JE. Moreover, with increase in translational energy, the .portion converted into excitation energy, as consistent with energy and momentum conserv­ ation, would become such that the complex lifetime would decrease to the duration of one vibrational period and the complex will simply cease to form. U sing the repulsion method we shall have, in this case,

(xv)

where Et(cr) is the translational energy value above which the complex is not formed. Here, 12/11 "' 1/Et. Thus, a possible approach to the problern of strong dependences of phenomenological cross-sections on particle rates may depart from the translational-excitational energy conservation concept. It would be ofinterest to undertake systematic experiments within a range of rather high translational energies and attempt to apply the external ionization method that would emphasize the relations of interest. Thus, the treatment of an ion-molecular elementary act as consisting of two steps, that of activated complex formation competing with the resonance charge exchange, and that of the complex decomposition, seems tobe justifi­ able and permits the definition ofpossible ways ofapproaching experimental and theoretical problems. The attention paid in this lecture to uncertain and unsolved problems of the ion-molecular reactions theory should not be considered as evidence for complete lack of clear understanding in this field. On the contrary, during the relatively few years of extensive investigations on this topic we seem to have acquired more knowledge than that available in the classical kinetic studies of neutral particles. Indeed, a precise qualitative picture of the reaction mechanism, knowledge of the activation energy (or, as a rule, of its absence), of the conformity of theoretical and experimental reaction rate constants, with an accuracy to within a factor of 2-3, etc., might be considered as a great success in any kinetic investigations. However, we should strive for a broadening of our ideas in this field for two reasons. First, ion-molecular reactions, due to their large cross-sections and to the possible use of the mass spectrometric technique, seem to be the only kinetic means yet available of carrying out investigations by the single­ collision method, as is the practice in nuclear physics. The application of this technique w-0uld make possible the accumulation of evidence on the nature of elementary acts to a degree undreamed of in normal kinetic studies of neutral particles. At the same time, it is possible that many features of ion-molecular reactions are displayed by other reactions as well. Perhaps insufficient attention is paid to the formation of relatively long-lived com­ plexes in reactions involving neutral particles. Perhaps by assuming the possible formation of such a complex in many reactions obeying Polanyi's rule, some new light might be thrown upon this rule. tConclusions in part similar to those given here have been arrived at by Moran and Hamill. 473 V. L. TALROSE The second reason for perfecting ion-molecular investigations is the need for rate eonstant values eonsiderably more precise than those required in neutral particle kineties, as the difference in rate eonstants of various exo­ therrnie ion-molecular reactions is considerably smaller than with exotherrnie reactions involving neutral particles. However, these small differenees are those aecounting for the modes of complex reactions involving ion-molecular elementa.ry steps.

THE APPLICATION OF DATA ON ELEMENTARY ION­ MOLECULAR REACTIONS IN VARIOUS FJELDS OF THERMODYNAMICS AND GAS PHASE KINETICS Let us now make certain necessarily brief statements as to the part played by elementary ion-moleeular reaetions in various fields of thermodynamics and gas phase kinetics, and discuss the conclusions arrived at, as weil as the possible methodological applieations of these eonclusions.

Application of results on ion-molecular reactions in investigating heats of formation and bond energies Investigations on elementary ion-moleeular reaetions resulted in the developrnent of a new method for determining these fundamental thermo­ ehemieal values, namely the ion-impact method. Reaeti.on rate constants not lower than I0-12 to I0-13 cm3 /sec may be determined using single-collision methods. The mere possibility of observing a reaction involving very slow ions shows that it proceeds without activation energy (to within 2-3 kcalfmole) and, consequently, may be considered as exothern1ic or thermoneutraL This 1nakes possible the derivation of corresponding thermochemical inequalities for heats of formation and bond energies. For example, Franke­ vieh and the author43 found that process (34) is observ.able; this means that the proton affinity of water is

Ei is the ionization potential and D the bond energy. Several laboratories have used this method to determine limiting values for proton a:ffinities and energies ofH atom abstraction foranurober of eases. In using this method for Hand H+ transfer, we further postulated43 that a reaction unobservable in a mass-spectrometer may be eonsidered as endothermic. Such an extension of the method's principle was, of course, of an empirical nature. I t was based on the fact that it appeared to be justified in about 70 reactions investigated, with the exception of rare cases when the transfer reaetion was not observed, but a competing reaction between the 74 same particles occurred. This problern became a subject of diseussion 9•20• - 76, arising in part through misunderstanding, and the only thing that need be said at present is that while the " first part" of the method is unquestionably 474 ION-MOLECULAR REACTIONS IN GASES adequate for all cases, the "second" should be used cautiously and, at the very least, requires strong evidence for the absence of competing reactions. Thus, Frankevieh and the author43 estimated the upper Iimit for proton affinity of water on the basis of the fact that processes

H 20 + NHt ----+ H 30+ + NH2 (35)

H 20 + C 2Hi ~ H 30+ + C 2H (36) were unobservable and, consequently, that

SH 0 < D(NH2 - H) + Ei(H) - Ei(NH ) = 184 kcaljmole 2 3

SH o ~ D(C H - H) + Ei(H)- Ei(C H ) = 171 kca1jmole 2 2 2 2 In the latter case secondary ions of a mass above 26 amu, which could have been produced by a competing reaction of H 20 with C 2Ht, were also undetectable. (The H atom transfer reaction H 20 + C 2H;t ---+ OH + C 2H{ is 31 kcaljmole endothermic.) Charge exchange involving slow ions is excluded in both cases being endothermic. Of interest are the proton affinity values for water and alcohols obtained by Frankevieh and the author43•77 using the ion impact method (Table 4). A systematic decrease in these values by 20 kcaljmole, as compared with the most reliable values obtained by indirect rriethods, will be noted78• Table 4. Proton affinities of water and alcohols determined by the ion impact method

j Calculated from data on Reactions for upper Limiting the crystal lattice energy, and lower Iimits values s without allowing for hydrogen bonding

H 0 H S+-+ H 0+ HS 167 2 + 2 3 + > 169 ± 2 188·6 H 20 + C2Ht +- H 30+ + C2H < 171

CH30H + H 20+ -+ CH30Ht + OH ;::,: 177 180 ± 3 209 CH30H + NHt +-+ CH30Ht + NH2 < 183

C2H 50H + H 20+ -+ C2H 50H;t + OH ;::,: 185 194 ± 9 216·5 C2H 50H + C6Ht +- C2H 50Hi + C6H 5 < 202

Sokolov and co-workers suggested later79 that by allowing for the hydrogen bond energy of an ionic crystal involving H 30+ ions, the proton affinity of water will also be decreased by 18 kca1jmole compared with the results of ref. 78. Speaking of" onium " ions it will be of interest to note that up to now the CHt ion discovered 10 years ago by Lyubimova and the author12 was the only product ever observed ofproton addition to a saturated hydrocarbon. An explanation for this might lie in the suggestion of Frankevieh and the 74 80 author • that the proton affinity of methane homologues is lower than that of methane (114-129 kcaljmole), which is, of course, astonishing, or it might lie in the idea of Lampe and Field81 that all reactions used for obtain!ng C 2Ht proceed by some competing and more probable ways. Lampe and Field infer the proton affinity of ethane from the reaction

CHt + CH4 --+ C2Ht + H 2 (37) 475 V. L. TALROSE which would proceed via the excited C 2Ht complex. On the basis of the fact that the heat of cornplex formation is somewhere between the heats of formation of initial and end products, they found that

244 > ~Hr(C 2 Hi) > 224 kcaljmole and

101 < S(C2H 6) < 121 kcalfmole

Finally, it may be emphasized that a very important and useful feature of the ion impact rnethod is the possibility it offers of estimating the proton affinity of saturated compounds; this cannot be measured by other direct experimental rnethods.

Charge exchange as a means of ionization in analytic mass spect:rometry The analytical mass spectrometry of multi-atomic molecules is often confronted with the requirement that ionization be produced without, or almost without, dissociative ionization.

Charg,e exchange ionization Ionization by electron impact 00 ...... 11'1 ......

~ 1 ~ > 1 ~

o; I' I I ~ a; I I' I : I I I ~ a:::ll I I : : : .: I II : . II I 0:: Y-f~~_,.._-t'-t-L-i.L.. ~J, ~ l 6 J, r.L J, J, J, J.. J, J, th J.. t.O...:t ...;t ..;t ...;t M M MN N N N N .-.- MaSS number Figure 10. Camparisan of hydrazine and acetone mass spectra obtained by charge exchange involving NHt ions and by 60 eV electron impact

A most popular method meeting this requirement isthat ofionization with 82 low-voltage electrons (Eltenton ) (see also refs. 83 and 84). At the sametime attempts have been made to devise other methods for obtaining "single­ line" and "few-line" spectra, such as the methods of photoionizationso,sa 87 and ionization in a strong electric field • The charge exchange method is also proruising in this respect. Lindholm35 discussed the possible application ofresonance charge transfer. The author38•88 noted that the great number of multi-atomic ion Ievels, and also the ready conversion of translational into excitational energy in charge exchange involving multi-atomic molecules, favours the use of the charge exchange method for obtaining "few-line" mass spectra; the bombarding ion should be selected here on the simple principle that

476 ION-MOLECULAR REACTIONS IN GASES where Ei is the ionization potential of the molecule, and Edi the potential of dissociative ionization yielding the ion to be avoided. We suggested the use of this method for mass spectrometric detection of free radicals when dissociative ionization is particularly undesirable. The mass spectra of (a) hydrazine and (b) acetone obtained by Lavrovs­ kaya, Markin and the author89 for charge exchange involving NHt ions are shown in Figure 10. The Jines for molecular ions are very intensive, while those for fragmentary ions are considerably weaker than in mass spectra of the same substances obtained by ionization with electrons of 60 eV. Consequently, the detection of free radicals in the presence of a large con­ centration of molecules is easier with "charge exchange" mass spectra. Mass spectra obtained in NHt charge exchange for products of pyrolysis of (a) hydrazine and (b) acetone from a reactor heated to 1,000° and located in the immediate vicinity of the charge exchange chamber, are shown in

Figure 11. The conclusion may be drawn from the observations that CH3CO and CH3 radicals are formed in acetone pyrolysis, while that of hydrazine yields N 2H 3 radicals and, probably, N 2H 2, N 2H, NH2 and NH.

---25°C ----- 1000°C

Acetone Hydrazine ..... kl ~ ...... :>..

i> 111 111 c c (]) (]) c I c ·- I I (]) (]) I > I .~ I I I I Cl! I I ~ I (]) (]) I I a: a: roM~mmro~w~~~ N~omro~w~ ~~~MNNNNN~~ MMMNN~~~ Mass number Figure 11. Mass-spectra ofhydrazine and acetone (fulllines) and pyrolysis products at 1000°, obtained by charge exchange involving NHt ions

Finally, let us note that charge exchange as a means ofionization seems to have been used for the firsttime by Dukelskii and Zandberg52 in obtaining negative oxygen ions by charge exchange involving Na-, K-, O-, OH-.

The radiation chemistry of gases The part played by ions in the radiation chemistry of gases attracted the attention of Lind as far back as 1920. The investigations carried out last year made possible a rational approach to obtaining a better insight into the part played by ion-molecular reactions in this field. Let us mention first the determination of the ion-molecular reactions responsible for the over-all process. This is done by analysis of the 477 V. L. TALROSE end products of radiolysis, with simultaneaus use of some method for pre­ dominant generation of a certain type of ions. We may mention here the work on oxidation carried out by Pshezhetzky and Dmitriev54 who deter­ mined the importance of the reaction

Nt + 0 2 ----*NO+ + NO (8) and its activation energy by making simultaneaus use of the critical potential method4 and kinetic analysis of the reaction rate temperature dependence. We may also mention the work of Lampe90 on radiolysis of a mixture of excess inert, or certain other, gases with H 2 and C 2H 4. Lampe suggested that atmnic hydrogen obtained by a reaction of the type

Ar++ H 2 ~ArH+ + H (32) was responsible for ethylene hydrogenation under these conditions. The i1nportant mass-spectrometric investigations mentioned above, and those con.cerned with ions yielded by bombardment of gas with electrons or ct-particles at pressures up to 0·5 mm Hg, should be recalled here. The lifetimes of intermediate complexes obtained by Field29 for ethylene and acetylene ( .-.10-7 sec) show the necessity of allowing for the reactions and stabilization of these complexes in working out mechanisms of complex radiation-induced reactions. Furthermore, studies may be mentioned which attempt to devise reaction schemes and compare the calculated and experimental values of end 56 9 products (Meisels, Hamill and Williams , Futrell \ Dorfman and Sauer92, Reinish 9 ~ 1 , etc). These authors combine the mass spectrometric data obtained, i.e. the yield in primary products of radiation-induced reactions, with data, and sometimes hypotheses, on possible secondary reactions involving ions and radicals. It will be noted that they use substances other than those of Melton's and Field's experiments, namely saturated hydrocarbons, for which the sequence of ion-molecular reactions appears to come to an end at the first or second step, since the next conceivable ion-molecular process will be endetherrnie and the ion recombination rate will exceed the rates of these processes. It is irnportant to note that satisfactory results may be obtained by this approach. This would seem to mean that the lifetimes of intermediate complexes in these systems are short. Let us recall that we are concerned with intermediate complexes of two types-the primary excited ions, and ion-molecular complexes. Consequently, both types should persist less than 10-9 to J0-10 sec. This is consistent with the conclusions of Tunitzky and co-workers72, 73 on very fast decomposition of ions in saturated hydrocarbons. On the other hand (as stated above) for markedly unsaturated ion­ molecular complexes, T ~ 10-7 sec, and as to primary excited ions, the question remains still unsettled. The importance of the problern of excited ion lifetirnes in radiation chemistry has recently been emphasized by Platz­ man94 and Stevenson9. The determination of ion lifetimes with respect to unimolecular decay of 1o-s to 1o-lO sec, and perhaps to even lower values, is a problem, the 478 ION-MOLECULAR REACTIONS IN GASES solution of which though difficult to realize, is fundamental for obtaining insight into the mechanism of high-pressure ion-molecular reactions and for the rational application of data obtained by using the single-collision method. The same may be said about measurements of the rates of reactions between molecules and the ions so recently formed. I t would also be desirable to extend mass-spectrometric investigations to within the atmosphere­ pressure range, the more so as this has already been achieved in investigating 95 96 the composition of ions in flames • • There has lately been a revival of interest in the part played by clusters in radiation induced gas phase reactions. This has been due, in part, to the experimental and theoretical studies on duster formation discussed in the preceding part of this paper. The change in ideas about the part played by clusters is of interest. In the early days of radiation chemistry clusters were considered to be responsible for higher radiation-induced yields, compared with ionic yields, whereas now there is every reason to believe that the occurrence of clusters in ion recombination decreases the probability of dissociation through chemical bonds. This is in part due to a decrease in the free energy of the system as a result of duster formation. Hence the process ...... j XY+·nM ~ + e = X + Y + nM (38) •...... ! Cluster

may even appear tobe endothermic. It is highly probable that even when there is enough energy the molecules will take up this energy by small por­ tions, and dissociation into X and Y radicals will not occur. (See Magee and Funabashi64 .) Burton97 reports that a decrease in radiolysis yields with a drop in ethane temperature down to the liquefaction point occurs in the gas phase, but under conditions close to the critical state. This he explains by the effect of clusters. Fiquet-Fayard98 suggested that the higher ion yields in water radiolysis ( as compared to the liquid phase) reported by Firestone99 are due to the decomposition reaction,

H 30+ + e~2H + OH (39) Pshezhetzky and the author100 consider this suggestion as scarcely possible, since at room temperature and pressures ofthe order ofO·l mm Hg, the water vapour ions will be present as strongly hydrated hydroxonium; this was shown recently by Knewstubb and Tickner101• It would be of interest to determine the behaviour of the ion-polymers which have been observed mass spectrometrically by Melton and Field at elevated pressures. A simultaneaus quantitative analysis of the end-polymers produced in radiolysis would be of considerable help.

Electric discharge Direct investigations dealing with the effect of ion-molecular reactions, and heavy ions in general, on themaindischarge characteristics are relatively 479

P.A.O. (VOL. 5. NOS. 3-4)-12 v~ L. TALROSE few. W~ may mention the well-known sturlies of Biondil02 on the effect of processes of the type

Ar* + Ar-~ Art + e (40)

Ar2 + + e -~Ar* +Ar (41) upon the rate of decomposition of the discharge plasma. Knewstubb and Tickner101 of Canada have reported recently on the predominant formation ofions H+·nH20(n = 1 ... 5) under a glow discharge in water at a pressure of 0·34 mm Hg. The question arises whether the part phiyed by minor water admixtures in the formation of free atoms in electric discharge is limited by the decrease in recombination activity at the wall? The processes :

Ht + H 2 -~Ht + H (1)

Ht + e -~ 3H or H 2 + H (42) are obviously very important for powerful ion sources in accelerators as main generators of atomic hydrogen which yields, in its turn, atomic ions

H + e-~H+ + 2e (43) ( see, in particular, reference 31). The inhibiting effect of charge exchange H+ + H = H + H+ in plasma investigated in connection with nuclear physics is weil known103• Finally, the relation between charge exchange and the effect of admixtures upon the work of discharge counters for fast particles104 was postulated long ago. An increase in interest in the direct investigation ofion-molecular reactions and heavy ions in discharges ofvarious types is tobe expected.

Ionosph€:ric processes It is a common belief nowadays that the important secondary processes occurring in the ionosphere, and which are to a considerable extent re­ sponsible for the attainment of its ionic balance, are, in fact, ion-molecular reactions1 [)5•106• In studying all possible exotherrnie reactions between 0~, O+, Nt, N+ 106 and 0 2, 0, N 2, N, Krassovsky reached the conclusion that the reaction

O+ + N 2 -~NO+ + N (44) plays an important part in the upper ionosphere, where primary ionization 8 3 1 is due to O+. The rate constant of this process is K 44 ~ I0- cm sec- and the heat of reaction + 0·83 e V. Determination of the effective recombination coefficient, under the assumption that reaction (44) is of predominant importance, provided an explanation for certain experimental results and led to the conclusion that this coefficient is dependent upon electron concentration. A more accurate and explicit study of the part played by reaction (44) in the establishment of the ionic balance of the ionosphere was carried out 480 ION-MOLECULAR REACTIONS IN GASES by Bagaryatzkii107• The results obtained were consistent with conclusions 106 drawn by Krassovsky • Bagaryatzkii showed that the N 2 concentration is the parameter responsible for probable variations in the nature of re­ combination with increase in altitude. Thus, although above 150 km the electron disappearance rate depends upon dissociative recombination with NO+ (as photorecombination with O+ will be ineffective under all con­ ditions) NO++ e--+N + 0 (45)

6 1 1 7 it will (K45 ~ I0- cms sec- ) 0 , yet at high altitudes (and lower N 2 content) be determined by the rate ofreaction (44). It will be noted, however, that the rate constant of reaction (44) may be considerably lower than I0-8 cm3 sec-1, as established by the work ofBates108•

Loaded ions in thermal equilibrium: ionization of gases Thermal ionization of gases is a process of great interest both from the theoretical and practical standpoints. The main experimental investigations on this topic are concerned with ionization in flames and, to a certain extent, in detonation waves. In the majority of cases, the systems studied are far from equilibrium, at least for neutral particles. However, a fundamental feature of these systems is beyond doubt, i.e. that the degree of gas ionization is higher than that corresponding to the Saha equilibrium equation, under the assumption that the ionization equilibrium is due to abstraction of electrons from neutral particles and recombination of electrons and ions,

M ~M+ + e (46)

The calculated value for the degree of ionization also appears to be lower than that observed experimentally when the particles considered are free radicals and atomst, and the high values of their non-equilibrium concentrations in fl.ames are taken into account. Various suggestions have been made as to the nature of "increased" ionization. The most justifiable for certain systems is the assumption that "loaded" ions, i.e. those possessing more atoms than the neutral particles, favour ionization on energetic grounds. This suggestion received direct confirmation in the recent experiments of Knewstubb and Sugden95•96•

These authors detected mainly H 30+ ions in the flame of hydrogen at a pressure of 1 atm. Thus, it is to be expected that the formation of" loaded " ions may be of importance in thermal gas ionization. However, it will be borne in mind that any process of formation of" loaded" ions from mole­ cules, for instance 2M~ M;t + e (47)

which is energetically more favourable than (46), would, nevertheless, be less favourable from the entropy standpoint. When the temperature increases and tlie relative effect of the correspond­ ing reaction heats on the degree of ionization becomes less marked (i.e. with increase in the importance of the en tropy factor), process ( 46), the routine t i.e. Particles having lower ionization potentials than those for saturated molecules. 481 V. L. TALROSE equilibrium ionization, will be responsible for the degree of ionization. Thus, the most pressing problern is that of finding out whether this temperature range is attained before or after ionization becomes important in some respect or other. 12

..... ~ / ~ I/ / "''/ /_ / I)/

1000 2000 3000 4000 5000 Temperature °K

Figure 12. Equilibrium ionization ofH20 vapour: ---over-all concentration accounting for H 30+ formation; ---- without H 30+ formation

Larin and the author109 evaluated various ionization equilibria taking into account the formation of "loaded" ions. Mass spectrometric results on the forrnation of secondary ions were used for obtaining heats of reactions. Calculated data for water, hydrogen and argon are shown in Figures 12 and 13. The concentration of" loaded" ions from thermal ionization, over a certain temperature range, may be seen to exceed considerably that of all other positive ions and be responsible for the concentration of free electrons and, consequently, for the gas conductivity at the given temperature. The excess of "loaded" ions over the maximum concentration of charged particles amounts to "' 3 orders of magnitude for water at 2,000°K, and about 3·5 orders for argon at 2,500°K.

14 ~ 12 ~ ~ ~ .... v c ~ / ~10 / c 8 ~1' / CLt /I ~ 6 !ft 0 0 lJ I '();4 V/ E 2 ~ lA'!'l Arj (Hfrt 1000 2000 3000 4000 5000 6000 TemperO.ture °K

Figure 13. Equilibrium ionization of H 2 and Ar: --- accounting for Ht formation; - - - - without accounting for H 3 +

It is interesting to note that in the curve for the over-all concentration of ions in water the ion concentration does not increase with temperature from 3,500 to 4,500°K, and perhaps even decreases. This is accounted for by the effect of neutral dissociation reactions on the formation of H 30+. 482 ION-MOLECULAR REACTIONS IN GASES The calculated equilibrium ionization values, taking into account the 8 3 formation of H 3Q+ ions (2·5 x 10 l/cm at I atm and 2,300°K) appear tobe close to the value obtained mass spectrometrically by Knewstubb and 101 9 3 Sugden forahydrogen ftame (10 1/cm ). Another process that occurs in hydrogenfoxygen mixtures, and which is very important in connection with the equilibrium formation of H 30+, is

(48)

Thus, if we consider the combustion of a mixture with the compos1tlon investigated, for instance of 98 per cent of oxygen, the resulting equi1ibrium concentration of H 3Q+ will be very close to the experimental value. As stated before, and as is evident from the curves ofFigure 12, at sufficiently high temperatures there is no necessity to allow for the concentration of loaded ions in calculating the over-all equilibrium ion concentration. How­ ever, the importance of the formation of such ions for states far from equi­ librium and, particularly, for the kinetics ofthe process leading to equilibrium, may be very great. For example, when the pre-exponential factors ofthe rate constants for reactions

Ar* + Ar = Ar+ + Ar + e (49)

Ar* + Ar = Art + e (50) are similar and the activation energies for these reactions are equal to their heatst (fl.H48 = -15·8 eV; fl.H49 ~ - 11·49 eV), the ratios of their rates will be 2·3 X 104 at T = 5000°K and 1·5 x 102 at T = 10,000°K. Thus, even at very high temperatures, when ionization is due solely to Ar+, the formation of the latter will proceed via the Art formation step.

Surface ionization and " loaded " ions Gomer and Inghram discovered several years ago87 that in a strong electric field created close to the surface of a very fine tip, the ionization may proceed with molecules of very high ionization potentials. Beckey and 110 Groth found recently that the ions emitted from such a source in CH30H ionization are in fact CH30H1 ions. Thus it appears that reactions of the type XH+YH=XHt+Y+e (51) which are thermodynamically more favourable than simple ionization, occur at the surface. It was found recently at Ionov's laboratory of the Leningrad Physico­ technical lnstitute111 that metallic surfaces heated to relatively low temper­ atures emit certain heavy ions, apparently of an organic nature (oil-vapour pumps were used in this work). The author believes that this interesting. phenomenon can scarcely be explained without invoking certain processes of associative ionization. The endothermic heat of these processes will be even lower because of the electron or radical affinity of the surface.

t This is true as inverse recombination reactions are not activated. 483 V. L. TALROSE To the extent of his capabilities and the time available the author has attempted to emphasize the essential results and trends of recent researches into ion-Inolecular reaction investigations; it is a fascinating field of chemical kinetics, and is highly favourable for combined studies of elementary and complex :reactions. The author would like to acknowledge the help of his colleagues: Mrs Lavrovskaya, Messrs Frankevich, Markin, Skurat, Karachevtzev, and Larin, and Miss Kritzkaya, and to thank Academician Kondratiev for valuable discussions. Let them accept rrry most sincere thanks.

References 1 H. D. Smyth. Phys. Rev. 25,452 (1925). 2 S. G1asstone, K. J. Laidler, and H. Eyring. The Theory of Rate Processes McGraw-Hill Book Co., New York, London (1941); H. Eyring, J. 0. Hirschfelder, and H. S. Tay1or. J. Chem. Phys. 4, 479 (1936). 3 S. C. Lind. The Chemical Effects ofrx-Particles and Electrons Chemica1 Cata1og Co., New York (1928). 4 0. H. Wansbrough-Jones. Proc. Roy. Soc. A127, 511 (1930); L. A. M. Henry. Bull. soc. chim. Belg. 40, 371 (1931). ~> H. Essex. J. Phys. Chem. 58, 42 (1954); H. Essex and D. Fitzgerald. J. Am. Chem. Soc. 56, 65 (1934); C. Smith and H. Essex. J. Chem. Phys. 6, 188 (1938); N. T. Williams and H. Essex. J. Chem. Phys. 17, 995 (1949). 6 M. M. l\1:ann, A. Hustrulid, andJ. R. Tate. Phys. Rev. 58, 340 (1940). 7 G. C. Eltenton. Nature 141, 875 (1938). s V. N. Kondratiev and G. C. E1tenton. Report NA 1/152, Institute of Chemica1 Physics of the USSR Academy of Seiences (1936). 9 D. P. Stevensou and D. 0. Schissler. "Mass spectrometry and radiation chemistry ", in collected works: Actions chimiques et biologiques des Radialions pp. 169-270, V ser, Paris­ Londres (1961). 1o R. E. Fox, W. M. Hickam, T. Kjeldaas, and D. J. Grove. Phys. Rev. 84, 859 (1951). 11 E. L. Frankevieh and V. L. Ta1rose. Pribory i Tekh. Eksp. No. 2, 48 (1957). 12 V. L. Talrose and A. K. Lyubimova. Doklady Akad. Nauk SSSR 86,909 (1952); V. L. Ta1rose. Thesis Institute of Chemical Physics, USSR Academy of Seiences ( 1952). 13 N. E. Alexeevskii, V. L. Talrose and V. N. Shelyapin. Doklady Akad. Nauk SSSR 93,997 (1953). u N. E. Alexeevskii, G. I. Kossourov, G. P. Prudkovskii, and S. I. Filimonov. Doklady Akad. Ni.zuk SSSR 100, 229 (1955). 15 D. 0. Schissler and D. P. Stevenson. J. Chem. Phys. 23, 1353 (1955); 24, 926 (1956). 16 D. 0. Schissler and D. P. Stevenson. J. Chem. Phys. 29, 282 (1958). 17 G. Gioumousis and D. P. Stevenson. J. Chem. Phys. 29, 294 (1958). 18 F. H. Field, F. L. Franklin, and F. W. Lampe. J. Am. Chem. Soc. 78, 5697 (1956). 19 F. H. Field, J. L. Franklin, and F. W. Lampe. J. Am. Chem. Soc. 79, 2665 (1957). 20 J. L. Franklin, F. H. Field, and F. W. Lampe. Advances in Mass Spectrometry p. 308, Pergarnon Press, London (1958). 21 V. L. Talrose and E. L. Frankevich. Report on the VIII Mendeleev Conf. Pure and Appl. Chem. Collected Abstracts No. 12, p. 59 (1959). 22 V. L. Talrose and E. L. Frankevich. lzvest. Akad. Nauk SSSR, Otdel. Khim. Nauk No. 7, 1351 (1959). 23 V. L. Talrose and E. L. Frankevich. Zhur. Fiz. Khim. 34, 2709 (1960). 24 M. I. Markin, G. V. Karachevtzev, and V. L. Talrose. /zvest. Akad. Nauk SSSR, Otdel. Khim. Ni.zuk No. 8, 1528 (1961). 25 R. S. Rudolph and C. E. Melton. J. Chem. Phys. 30, 847 (1959). 26 C. E. Melton and R. S. Rudolph. J. Chem. Phys. 32, 1128 (1960). 27 R. S. Rudolph and C. E. Melton. J. Phys. Chem. 63, 916 (1959). 28M. Saporoshchenko. Phys. Rev. 111, 1550 (1958). 484 ION-MOLECULAR REACTIONS IN GASES

29 F. H. Field. J. Am. Chem. Soc. 83, 1523 (1961). 3° C. E. Melton. ]. Chem. Phys. 33, 647 (1960). 31 H. S. \V. Massey and E. H. S. Burhop. Electronic and Ionic Impact Phenomena Oxford University Press (1952). 32 J. B. Hasted. Proc. Roy. Soc .. A205, 421 (1951). 33 I. V. Fedorenko. Uspekhi. Phys. Nauk 68, No. 3, 481 (1959). 34 Ya. M. Vogel. Uspekhi. Phys. Nauk 71, 243 (1960). 35 E. Lindholm. ,Z. Naturforsch. 9a, 535 (1954). 36 E. Lindholm. Proc. Phys. Soc. (London) A66, 1068 (1953); Applied Mass Spectrometry Report of a Conference (1953) organized by the Mass-Spectrometry Panel of the Institute of Petroleum, p. 191, London ( 1954). 37 E. Lindholm. Arkiu. Fysik. 8, 257 (1954); 8, 433 (1954); H. von Koch and E. Lindholm. Arkiu. Fysik. 19, 123 (1961); E. Gustafsson and E. Lindho1m. Arkiv. Fysik. 18, 219 (1960). 38 V. L. Talrose. USSR Patent No. 121577, 14.3.1958. 39 V. L. Talrose, L. L. Dekabrun, G. D. Tantzyrev, E. L. Frankevich, 0. D. Vetrov, A. K. Lyubimova, V. D. Grishin, V. I. Erofeev, G. K. Lavrovskaya, V. E. Skurat, and Ya. A. Yukhvidin. USSR Patent No. 121965, 14.3.1958. 40 Mass Spectrometer for Determination of Free Radicals Brussels Universal and International Exhibition, Vneshtorgizdat, 1958, USSR section. 41 V. L. Talrose. Proc. All-Union Corif. Electron and Ion Collisions, Ist Conf. Riga, 26 June- 3 July (1959); Izuest. Akad. Nauk SSSR, Ser. Fiz. 24, 1001 (1960). 42 V. L. Talrose, L. L. Dekabrun, E. L. Frankevich, G. D. Tanzyrev, 0. D. Vetrov, A. K. Lyubimova, G. K. Lavrovskaya, V. D. Grishin, V. I. Erofeev, V. E. Skurat, and Ya. A. Yukhvidin. Pribory i Tekh. Eksp. No. 6, 87 (1960). 43 V. L. Talrose and E. L. Frankevich. Doklady Akad. Nauk SSSR 111, 376 (1956). 44 F. H. Field and F. W. Lampe. J. Am. Chem. Soc. 80, 5587 (1958). 45 R. P. Pottie, R. Bark er and W. H. Hamill. Radiation Research 10, 664 ( 1959). 46 T. R. Hogness and R. W. Harkness. Phys. Rev. 32, 784 (1928). 47 R. P. Pottie and W. H. Hamill. J. Phys. Chem. 63, 877 (1959). 48 E. E. Muschlitz, Jr. J. Appl. Phys. 28, 1414 (1957). 119 A. Heng1ein and G. A. Muccini. J. Chem. Phys. 31, 1427 (1959). 50 H. KaUmann and B. Rosen. ,Z. Physik. 61, 61 (1930); 64, 806 (1930). 51 G. K. Lavrovskaya, M. I. Markin, and V. L. Talrose. Kinetics and Catalysis 2, 21 (1961). 53 V. M. Dukelskii and E. Ya. Zandberg. Doklady Akad. Nauk SSSR 82, 33 (1952). 53 V. L. Talrose and E. L. Frankevich. Goileeted papers ofthe Ist All-Union Conference on Radiation Chemistry, Acad. Sei. USSR, p. 13, Moscow (1958). 04 S. Ya. Pshezhetzky and M. T. Dmitriev. Doklady Akad. Nauk SSSR 103, 647 (1950); Effect oJ lonizing Radialions on Inorganic and Organic Systems (Russ), Moscow, USSR Acad. Sei., p. 145 (1958). 55 V. Cermak and Z. Herman. J. chim. phys. 51, 717 (1960). 56 G. G. Meisels, W. H. Hamill, and R. R. Williams Jr. J. Phys. Chem. 61, 1456 (1957). 57 R. E. Fox, W. M. Hickam, and T. Kjeldaas. Phys. Rev. 89, 555 (1953). 58 G. G. Meisels. J. Chem. Phys. 31, 284 (1959). 59 M. Herzberg, D. Rapp,J. B. Ortenburger, and D. D. Briglia. J. Chem.Phys. 34,343 (1961). 60 L. D. Landau. Physik. z. Sowjetunion 2, 46 ( 1932). 61 C. Zener. Proc. Roy. Soc. (London) A137, 696 (1932). 6 z H. B. Rasted and J. B. Gilbody. Proc. Roy. Soc. (London) A238, 334 (1957). 63 Yu. F. Bydin and A. M. Bukhteev. ,Zhur. Tekh. Fiz. 30, 546 (1960). 84 J. L. Magee. J. Phys. Chem. 56, 555 (1952). 64 & J. L. Magee and K. Funabashi. Radiation Research 10, 622 (1959). 65 V. L. Talrose. Report an the Symposium an Chemical Effects of Nuclear Tran~formations Praha, October (1960). 66 G. V. Karachevtzev, M. I. Markin, and V. L. Talrose, to be published. 67 E. L. Frankevich. Thesis, Institute of Chemical Physics, USSR Academy of Seiences (1956). 68 E. F. Gurnee andj. L. Magee. J. Chem. Phys. 26, 1237 (1957). 69 P. Langevin. Ann. chim. et phys. 5, 245 (1905). 70 H. Gutbier. ,Z. Naturforsch. 12a, 499 (1957). 485 V. L. TALROSE 71 H. M. Rosenstock, M. B. Wallenstein, A. L. Wahrhaftig, and H. Eyring. Proc. Natl. Acad. &i. U.S. 38, 667 (1952). 72 N. N. Tunitzky. Intern. Congr. Pure and Appl. Chem. 18th Congr. 1961, Montreal, Section IA. Report. 73 M. V. Guriev, M. V. Tikhomirov, and N. N. Tunitzky. Doklady Akad. Nauk SSSR 126, 120 (1958); Zhur. Fiz. Khim. 32, 2721 (1958); V. K. Potapov, V. G. Vassiliev, and N. N. Tunitzky. Problems Phys. Chem. (Russ.), No. 2, Moscow, Goskhimizdat (1959). 74 V. L. Talrose and E. L. Frankevich. J. Am. Chem. Soc. 80,2345 (1958). 76 F. W. Lampe and F. H. Field. Zhur. Fiz. Khim. 33, 732 (1959). 76 V. L. Talrose and E. L. Frankevich. ,Zhur. Fiz. Khim. 33, 955 (1959). 77 E. L. Frankevieh and V. L. Talrose. Z,hur. Fiz. Khim. 33, 1093 (1959). 78 V. N. Kondratiev and N. D. Soko1ov. Zhur. Fiz. Khim. 29, 1265 (1955). 79 S. I. Vetchinkin, E. A. Pshenichnov, and N. D. Soko1ov. Zhur. Fiz. Khim. 33, 1269 (1959). 80 E. L. Frankevieh and V. L. Ta1rose. Doklady Akad. Nauk SSSR 119, 1174 (1958). 81 F. W. Lampe and F. H. Field. J. Am. Chem. Soc. 81, 3242 (1959). 82 G. C. Eltenton. ]. Chem. Phys. 10,403 (1942); 15,455 (1947). 83 F. H. Field and S. H. Hastings. Anal. Chem. 28, 1248 (1956). 84 H. E. Lumpkin. Anal. Chem. 30, 321 (1958). 85 F. P. Lossing andj. Tanaka. J. Chem. Phys. 23, 1031 (1956). 86 F. I. Vilessov. Doklady Akad. Nauk SSSR 132, 1332 (1960); F. I. Vi1essov, B. L. Kurbatov, and A. N. Terenin. DokladyAkad. NaukSSSR 122,94 (1958). 87 R. Gomer and M. G. Inghram. J. Am. Chem. Soc. 77, 500 ( 1955); ]. Chem. Phys. 22, 1279 ( L954). 88 V. L. Talrose. Pribory i Tekh. Eksp. No. 5, 116 (1957). 89 G. K. Lavrovskaya, M. I. Markin, and V. L. Talrose. Proc. All-Union Corif. Ana(ysis of Organic Substances Moscow, (1961). 9° F. W. Lampe. J. Am. Chem. Soc. 82, 5551 (1960). 91 J. H. Futrell. J. Am. Chem. Soc. 81, 5921 (1959). 92 L. M. Dorfman and C. M. Sauer. J. Chem. Phys. 32, 1886 (1960). 93 L. Reinisch. J. chim. phys. 57, 1060 (1960). 94 R. L. Pllatzman. Discussion at the Lind Symposium of the Radiation Research Society, Pitts- burgh, May 1959 (see ref. 9, p. 253). 95 P. F. Knewstubb and T. M. Sugden. Proc. Roy. Soc. (London) A255, 520 (1960). 96 P. F. Knewstubb and T. M. Sugden. Nature 181, 1261 (1958). 97 M. Burton. Z· Elektrochem. 64:, 975 (1960). 08 Mme F. Fiquet-Fayard. J. chim. phys. 51, 453 (1960). 99 R. F. Firestone. J. Am. Chem. Soc. 79, 5593 (1957). 100 S. Ya. Pshezhetzky and V. L. Talrose. Proc. All-Union Corif. Radiation Chem., 2nd. Moscow, October ( 1960)-in print. 101 P. F. Knewstubb and A. W. Tickner. Report on the 8th Annual Meeting of the A.S. T.M. Committet· E14 on Mass Spectrometry Ottawa, June (1960). 102 M. A. Biondi. Appl. Spectroscopy 11, 119 (1957). 103 A. Bishop. " Serwood Project ", U.S.A. Program on Controlled Thermonuclear Synthesis Atomizd.at Moscow, page 113 (1960); G. I. Budker. "Physics of plasma and problems of controlled thermonuclear reactions" (Russ), lzvest. Acad. Nauk SSSR 3, 19 (1958). 104 S. A. Korffand R. D. Present. Phys. Rev. 65, 274 (1944). 10 5 D. K. Bates. Proc. Phys. Soc. (London) 68A, 344 (1955). 106 V. I. Krassovsky. lzvest. Akad. Nauk SSSR, Ser. Geofyz. No. 4, 504 (1957). 107 B. A. Bagaryatzkii. lzvest. Akad. Nauk SSSR, Ser. Geifyz. No. 9, 1359 (1959). 108 D. R. Bates and M. Nicolet. J. Atmospheric and Terrestl. Phys. 18, 65 (1960). 109 I. K. Larin and V. L. Ta1rose. Kinetika i Kataliz 3, 305 (1962). 110 H. D. Beckey and W. Groth. z. phys. Chem. 20, 37 ( 1959); H. D. Bec~ey. ,Z. Natuiforsch. 15a, 822 (1960). 111 E. Ya. Zandberg. Zhur. Tekh. Fiz. 30, 206 (1960).

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