Reactions of C+ Ions with Some Methyl HalidesPatricia Sullivan Wilson, R. W. Rozett, and W. S. Koski Citation: The Journal of Chemical Physics 53, 3494 (1970); doi: 10.1063/1.1674523 View online: http://dx.doi.org/10.1063/1.1674523 View Table of Contents: http://scitation.aip.org/content/aip/journal/jcp/53/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Reactions between cold methyl halide molecules and alkali-metal atoms J. Chem. Phys. 140, 014303 (2014); 10.1063/1.4834835 Interaction of gaseous D atoms with alkyl halides adsorbed on Pt(111), H/Pt(111), and C/Pt(111)surfaces: Hot-atom and Eley–Rideal reactions. I. Methyl bromide J. Chem. Phys. 111, 3209 (1999); 10.1063/1.479600 An ion beam study of reactive scattering of halide ions by methyl halides J. Chem. Phys. 80, 1108 (1984); 10.1063/1.446839 The Reaction of Methyl Radicals with Some Halogenated Methanes J. Chem. Phys. 20, 578 (1952); 10.1063/1.1700496 The Potential Functions of the Methyl Halides J. Chem. Phys. 7, 522 (1939); 10.1063/1.1750481

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3494 PLATO, HARTFORD, AND HEDBERG

by the method previously described [M. Iwasaki and K. Hedberg, J. Chern. Phys. 36,2961 (1962)J, and (,)=0.00503, (M')= 0.00121 [K. Kuchitsu, Bull. Chern. Soc. Japan, 40, 505 (1967) J.

9 G. Gundersen and K. Hedberg, J. Chern. Phys. 51, 2500 (1969) .

10 K. Hedberg and M. Iwasaki, J. Chern. Phys. 36,589 (1962). 11 To obtain the data for these curves order Document No.

NAPS-01084 from National Auxiliary Publications Service of the ASIS, clo CCM Information Corp., 909 Third Ave., New York, N.Y. 10022, remitting $2.00 for microfiche or $5.00 for photo­copies.

12 The modified scattering amplitudes Ai and phases 1Ji used throughout this work were obtained from Cox and Bonham's tables [H. L. Cox and R. A. Bonham, J. Chern. Phys. 47,2599 (1967) J by the procedure described in Ref. 8.

13 K. Hedberg and M. Iwasaki, Acta Cryst. 17, 529 (1964). 14 L. Hedberg, R. R. Ryan, and K. Hedberg (unpublished). 16 This is to say that about equally good fits are obtained by

combining larger (smaller) distance differences with smaller (larger) amplitudes.

16 According to significance tests [W. C. Hamilton, Acta Cryst. 18, 502 (1965) J the rejection of models C and F in favor of E has an error probability of about 50%. The error probability in a rejection of D is of course even higher.

17 These values are obtained by adding V2XO.0009 A and -V2XO.0016 A, respectively, to the N-F and 0··· F amplitudes; the factor V2 takes into account the effect of possible correlation among the observations. Use of <Tl, instead of a larger quantity containing estimates of systemactic error seems justified: Because the two amplitudes are similar, the systematic errors are likely to have similar effect on each. The independent treatment of the two amplitudes is indicated by the very low correlation co­efficien t connecting them.

18 Y. Morino, K. Kuchitsu, and T. Oka, J. Chern. Phys. 36, 1108 (1962).

THE JOURNAL OF CHEMICAL PHYSICS

19 V. W. Laurie and D. R. Herschbach, J. Chern. Phys. 37,1687 (1962) .

20 Since Ya-Yo for single bonds between first-row atoms appears to be less than 0.003 A, a larger variation in r(~-F)IY(N=O) seems most unlikely. The approximation is probably even better for dO···F)lr(F·· ·F) because of the geometrical similarity of the two distances; in any event it is not especially limiting since an error of 0.003 in one of the ratios corresponds to only 0.10 in the ONF angle.

21 For example, in BF3 ra(B-F) -ro(B-F) =0.0024±0.0008 A. See K. Kuchitsu and S. Konaka, J. Chern. Phys. 45,4342 (1966).

'2 A more correct approach to the entire problem would use the spectroscopic and diffraction data, each properly weighted, in a least-squares procedure to find the best estimates of all parameter values [K. Kuchitsu, T. Fukuyama, and Y. Morino, J. Mol. Struct. 1, 463 (1967)].

'"V. Schomaker and D. P. Stevenson, J. Am. Chern. Soc. 63, 37 (1941).

24 The bond numbers were estimated from the formula D(n) = D(l) -c 10g1J with c=0.60 and 0.71 for the N-F and N=O bonds, respectively. See L. Pauling, The Nature of the Chemical Bond (Cornell U. P., Ithaca, N.Y., 1960), Chap. 7.

25 A. Caron, G. J. Palenik, E. Goldish, and J. Donohue, Acta Cryst. 17, 102 (1964).

26 J. Sheridan and W. Gordy, Phys. Rev. 79, 513 (1950). 27 D. R. Lide, Jr., J. Chern. Phys. 38,456 (1963). 28 L. Pierce, R. G. Hayes, and J. F. Beecher, J. Chern. Phys.

46, 4352 (1967). 29 D. P. Craig, A. Maccoll, R. S. Nyholm, L. E. Orgel, and

L. E. Sutton, J. Chern. Soc. 1954, 332. 30 D. W. J. Cruickshank (personal communication); 1,. S.

Bartell (personal communication). 31 R. J. Gillespie, Can. J. Chern. 39, 318 (1961); J. Chern. Soc.

1963,4676. 32L. S. Bartell, J. Chern. Phys. 32, 827 (1960).

VOLUME 53, NUMBER 9 1 NOVEMBER 1970

Reactions of C+ Ions with Some Methyl Halides*

PATRICIA SULLIVAN WILSON, R. W. ROZETT,t AND W. S. KOSKI

Department of Chemistry, The Johns Hopkins University, Baltimore, Maryland 21218

(Received 6 July 1970)

The reactions of C+ in the ground state with the methyl halides (CH3X) were studied in the 2-200-eV energy region using a tandem mass spectrometer. The cross sections as a function of ion kinetic energy were measured and used to infer reaction mechanism. Hydride ion, halide ion, carbanion as well as halogen atom and CHa pickup were dominant reactions at low energy. At higher energies dissociative anion pickup was an important mechanism for the formation of ions containing one carbon atom. The polarizability of the C-X bond and the energetics of the process appeared to be the most important factors dictating the course of the reaction.

INTRODUCTION

Recently we had occasion to study the reactions of C+ ions in the ground state with CH41 and CHaF.2 The dominant mechanism for the ion-molecule reactions that were observed appeared to be a stripping mecha­nism where the projectile ion picked up either a nega­tively charged or a neutral portion of the target molecule. In order to get a better insight into the nature of the mechanism of some of these reactions, it was decided to extend these studies to a related family of compounds whose polarizabilities and other proper­ties were known. This is a report of the results of such studies on the reactions of C+ in the 2p state with the methyl halides in the energy region of 2-200 eV.

EXPERIMENTAL

The tandem mass spectrometer used in this study has been described previously.3.4 It consists of two magnetic mass spectrometers in series. The first is a 180° magnetic sector instrument with a 1-cm radius of curvature. The secondary mass spectrometer, which analyzes the ionic products extracted from the reaction chamber, is a 60° magnetic sector instrument with an 8-in. radius of curvature. The pressure measurements in the reaction chamber were made with an MKS Baratron Type 77H-l pressure meter. Detection is made with a 17-stage electron multiplier. Individual ion counting techniques were used. The C+ ions were produced by electron bombardment of CO. Conditions were such in the ion

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REACTIONS OF C+ ION S 3495

TABLE r. Heats of reaction (eV) for the reaction of C+(2P) +CHaX.

Reaction products X=H F Cl Br I

C+CHaX+ -1.40 -1.58 0.06 0.74 1.72 CX+CHa+ 0.46 1.56 1.29 1.27 1.56 C+CHa++X -3.05 -3.74 -2.20 -1.55 -0.99 C+CH2X++H -3.05 -2.97 -2.53 -2.12 -2.14 CH+CH2X+ 0.46 0.54 0.06 1.39 1.37 C+CHa+X+ -6.82 -10.74 -5.37 -3.55 -1.64 C2Ha+X+ -0.75 -5.28 0.77 2.51 4.42 CH+CHX++H -4.97 -4.72 -4.60 -3.50 -2.54 CH2+CHX+ -0.57 -0.32 -0.20 0.90 1.66 CH++CH2X -0.83 -1.23 0.98 -0.97 -1.14 C+CH2++HX -3.96 -3.28 -3.15 -3.15 -3.33 CX+CH2++H -4.96 -3.87 -4.23 -4.13 -3.87 CHX+CH2+ -0.57 0.01 0.14 0.01 0.07 CX++CHa -0.83 2.2 0.03 0.88 2.40 C2Ha++X 4.0 3.30 4.90 5.50 6.06 C2H2++HX 4.18 4.84 5.0 4.95 4.80 C2H2X++H 4.0 2.95 4.36 4.71 5.23 C2HX++H2 4.18 2.39 3.51 4.31 4.35 C2H++H2+X -1.63 -2.34 -0.71 -0.14 0.42 C2H++HX+H -1.63 -0.95 0.75 -0.86 -1.01 C2H2+HX+ 0.14 0.46 3.71 4.73 5.79

source that the C+ ions were in the ground state (2P). All of the gases except CHal used were obtained from the Matheson Company and the CHal was obtained from the Fischer Scientific Company. All gases were checked for purity with an analytical mass spectrometer.

DISCUSSION

In the reaction of C+(2P) ions with the methyl halides the highest cross sections were observed for the parent ions CHaX+ of the higher methyl halides. These ions arise from charge transfer reactions and the probabilities for the process are summarized in Fig. 1, where the cross sections are plotted as a function of ion energy. The methyl fluoride ion behavior is one that may be expected for an endothermic charge transfer process. The cross section rises with energy and then goes through a broad maximum. The ionization poten­tial of methyl chloride is very nearly the same as that of the ground state of the carbon atom and the behavior of the cross section vs C+ ion energy probably represents the behavior of an accidentally resonant charge transfer process. The behavior of the methyl bromide and iodide is somewhat unexpected. Since the ionization potentials of CHaI and CHaBr are lower than that of C atom, the reactions are exothermic and the behavior of the cross section with energy in the low-energy region reflect this fact. The subsequent rise of the cross section in both the iodide and the bromide cases indicates the availability of new channels for reaction and suggests that transitions are taking place to excited states of the CHaX+ ions.

Also included in Fig. 1 are the cross sections for the production of CH2X+. The iodide is not included in

this plot because of lack of sufficient resolution by the secondary mass spectrometer. These reactions show a typical exothermic behavior, and consequently they do not arise from dissociative charge transfer reactions since all of these reactions are endothermic (Table I). Using arguments analogous to those used in inter­preting the corresponding results obtained for the reaction of C+ (2 P) with CH41 and CHaP, one concludes that these reactions are proceeding by hydride ion transfer,

C+(2P)+CHaX~CH2X++CH. (1)

In Fig. 2 the cross sections for the production of the CHa+ ion from the reaction of C+ with the methyl halide is presented. These reactions also show a typical exothermic behavior; consequently they are not charge transfer dissociation reactions in which the products are CHa+, X, and C since these are endothermic (Table I). Following the reasoning used in our study of the CH4

and CHaF reactions with C+, the most probable mechanism for CHa+ formation from CHaX molecules is halide ion transfer. In the higher-energy region, the cross section for the production of CHa+ increases as one substitutes the halogen on the methyl group from F to Cl, to Br, and finally to I, and this increase reflects the change in reaction cross section as the halide atom in CHaX is substituted. It appears, therefore, that the CHa+ ions arise from the reaction

C+(2P)+CHaX~CX+CHa+. (2)

Figure 2 also includes the cross sections for the produc­tion of ions of mass 13 and 14. It will be noted that the production of CH2+ no longer follows the simple order

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3496 WILSON, ROZETT, AND KOSKI

"\ 'L 10 \~

, ~ .. =--. -o~(J--L:::....-..o-o--o--~

0~~:2~0~~~40~~7~6~0====8~0===:;;~::::~ ION ENERGY (eV)

FIG. 1. Cross sections versus projectile ion kinetic energy for production of (1) CHaI+, (2) CHaBr+, (3) CHaCl+, (7) CHaF+, (4) CH2F+, (5) CH2CI+, and (6) CH2Br+ for the reaction of C+(2P) with the methyl halides.

of the CH3+ ions. This in some respects might be ex­pected since CH2+ can be produced in a variety of ways from CHaX by reaction with a C+ ion. Dissociative charge transfer and dissociative anion pickup are both very endothermic and hence are not candidate mecha­nisms at the low energy. However, at high energies, i.e., above about 30 eV, the dissociative anion pickup mechanism is an attractive one for the production of CH2+.1 In the low-energy region HX- and H2 pickup are possibilities since these reactions appear to be exo­thermic if the available thermodynamic data are correct. Because of the electrical nature of the process, the HX- pickup is the more attractive of the two mechanisms in the low-energy region.

Similar remarks can be extended to the production of CH+. The probability of neutral atom pickup is con­siderably smaller than negative ion pickup, so it is believed that the mechanism for production of CH+ in the high-energy region is very likely dissociative anion pickup. However, H atom pickup cannot be excluded in the low-energy region.

In Fig. 3 the reaction of C+(2P) with CHgX to produce X+ is illustrated. The 1+ ion is formed with a cross section of about 3-4 12, whereas Br+ has a cross section somewhat below 1 12, and Cl+ was barely detectable, and no F+ was observed. The experimental behavior of the cross sections for the first two reactions

indicate reaction exothermicity, and indeed the thermo­dynamic data show that all the reactions that give X+ are exothermic. The hydrogen and the fluorine cases do not react to give X+, and these are clearly endothermic. These reactions of C+ with the higher methyl halides can be represented by the equation

C+(2P) +CHgX~CCHg+X+. (3)

This reaction results from a carbanion transfer. This is not unreasonable since, if the C-X bond is sufficiently polarizable, the high electric field associated with the C+ ion polarizes the molecule sufficiently so that there is effectively a transfer of a CHg- group to the C+ with the corresponding production of X+. On the other hand, the course of the reaction is not solely dictated by bond polarizability since apparently reaction energetics forbid the reaction in the case of methane and methyl fluoride. The fact that in the CH4 case no H+ is observed is compatible with our earlier conclusions that under our experimental conditions there is a negligible amount of the C+ ions in the 4p state.1 It should also be borne in mind that in the higher-energy region X+ can also be produced by various dissociative processes of precursor ions containing the X atom.

Figure 3 also gives the cross section curves for the ions CHX+ which were observed in the cases of methyl

3.9.tt----------~""~---,l

3.0

2.0

oIO....!:!..A.---'L--_--=-_____ o ___ 0_0_0_2

_.,...-_-=-__ ....... __ tJ. ___ .6-r.:_._3

1.0 -O---cr--o---o--O-o~4

00 20 40 60 80 200 ION ENERGY (eV)

FIG. 2. Cross sections versus projectile ion kinetic energy for the production of CHa* from (1) CHaI, (2) CHaBr, (3) CHaCl, and (4) CHaF. (5), (6), (7), and (8) represent the cross sections obtained for CH2+ from CHaBr, CHaCl, CHaI, and CHaF, re­spectively. (9), (10), (11), and (12) indicate the curves for CH+ from CHaCl, CH3Br, CHaF, and CHaI, respectively.

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REACTIONS OF C+ IONS 3497

fluoride, chloride, and bromide. This ion is undoubtedly present in the CHaI case; also, however, the limiting resolution of the secondary mass spectrometer pre­vented the unambiguous measurement of this ion in that case. The CHF+ curve was typical of an endo­thermic reaction, whereas CHCl+ and CHBr+ yields gave exothermic behavior. Ions of this type could not be produced by a charge transfer dissociation process if C+ was in the 2p state. Assuming the absence of the 4p state, one can propose a mechanism in which the methyl end of CHaX is polarized by the C+ in such a way that H2- is transferred to the carbon forming CH2 with the resultant production of CHX+. This is the only process that can account for the observed exothermicity of the reaction. In the low-energy region we can represent these reactions by the equation

C+(2P)+CHaX~CH2+CHX+. (4)

In the higher-energy regions hydride ion pickup and subsequent dissociation of the resulting ion into CHX+ is the most attractive mechanistic mode.

Figure 3 also gives the yield curves for CBr+, CCl+, and CF+ from CHaBr, CHaCl, and CHaF, respectively. These curves exhibit a typical exothermic behavior. Consequently, in the low-energy region one postulates a halogen atom pickup mechanism,

C+(2P)+CHaX~CX++CHa. (5)

Our experimental observations show that these ions have considerable kinetic energy in the beam direction at low energies and are very likely being produced by

3.0 4.0

Br+ 1.0 \-o"'-~c-c-c,--,I---

40 80 120 160 200 ION ENERGY (eV)

°0~~~2~0~~4~0~~6~0~~8~0~~~\~~-=~

ION ENERGY (eV)

FIG. 3. Insert: cross sections versus projectile ion kirretic energy for the production of 1+ and Br+ from CHaI and CHaBr, respectively. Cross sections versus projectile ion kinetic energy for the production of (1) CHCl+, (3) CHBr+, (4) CHF+, (2) CBr+, (5) CCI+, and (6) CF+.

.8,-..,,---------i

3.0 CCHF +

1.0

FIG. 4. Cross sections versus projectile ion kinetic energy; upper half of figure: (1) CCH2+, (2) CCHa+, (3) CCH+, and (4) C2+ from CHaF. The results for the CCHF+ ion are given in the insert. The lower half of the figure gives corresponding results for CHaCl.

a stripping mechanism. This mechanism, on the other hand, cannot prevail in the higher-energy region since the internal energy in the product ion exceeds the dis­sociation energy and the ions will not form above a certain critical bombarding energy. Consequently, in the higher-energy region the ion probably results from one or more of the dissociative type mechanisms mentioned earlier. This is supported by the fact that in the higher-energy region the cross sections decrease as one proceeds in the series CBr+, CCl+, and CF+, whereas in the low-energy region the order is reversed.

Finally, ions containing two carbon atoms such as C2H,,+(x=3, 2, 1,0) and C2H.X+(x=2, 1,0) where X is a halogen atom were observed. These reactions represent the pickup of a neutral entity from the target molecule. The case of mass 27, i.e., CCHa+, will be considered first. The reactions producing this ion, assuming it has the structure of a vinyl ion, are all exothermic (Table I), which is compatible with the observed cross sections, and the process can be repre­sented by the equation

C+(2P)+CHaX~CCHa++X. (6)

The cross section is highest in the fluoride case (Figs. 4 and 5) and falls approximately inversely as the

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3498 WILSON, ROZETT, AND KOSKI

2.0- CH3Br

00 '0 20 30 40 50 ION ENERGY (eV)

FIG. 5. Cross sections versus projectile ion kinetic energy for CHaBr and CHa!. (1) CCH2+, (2) CCHa+ (3) CCH+ and (4) CC+. "

polarizability of the C-X bond as one goes through the series from fluoride to iodide. CHa pickup is most probable in the target molecule that provides the least probability of CHa- pickup. There appears to be a competition between CHa and CHa- pickup. Which reaction takes place depends on the polarizability of the target molecule and on the energetics of the reaction.

The production of the ion CCH2+, mass 26, is also an exothermic reaction and may be represented by the equation

C+(2P)+CHaX~CCH2++HX. (7)

We assume that the heat of formation of this ion is the same as that of the acetylene ion. This reaction has a higher cross section than the one giving CCHa+, and this probably arises from the greater stability of CCH2+ because of the possibility of multiple bonding in this ion. Again at low energies the cross sections for the produc­tion of CCH2+ from the various methyl halides studied vary approximately inversely as the polarizability of the target molecule. At projectile energies above about 15 lteV:the differences in the cross sections for the production of CCH2+ from)he various methyl halides becomes smaller and the order tends to reverse when compared to the low-energy region. Figure 6, where log of cross section versus log of projectile ion kinetic energy is plotted, illustrates these points. It will be further noted that the energy dependence of the cross section is very much steeper in the higher-energy region. This suggests that in this energy region some type of rebound mechanismS is dominating the reaction as contrasted with a simple stripping mechanism which seems to be operating in the energy region below 10 eV. The critical energy expected from simple stripping theory is less than 10 eV. Consequently, the ionic

products observed would not be expected to exist at the higher energies if stripping was the sole mechanism operating.

The mass 25 ion, CCH+, has behavior similar to that of the mass 26 ion; however, its cross sections are 7-9 times smaller. Again, the cross section falls with the inverse polarizability and this fall has approximately the same slope as the fall for the mass 26 ion. The mass 24 ion is also present but even in smaller abundance than the mass 25 ion. In view of the similar dependence of the two carbon ions on the polarizability of the target molecule, one is tempted to propose that this category of two carbon ions may be related through a dissociative process. Such a mechanism is CHa pickup followed by dissociation,

C+(2P)+CH3X~CC+Ha+X (8)

1 CCH2+

1 CCH+

1 cC+.

However, it is difficult to establish this connection unambiguously from the data obtained in this study.

There were also two other carbon ions produced. These ions were of the type CCH2X+, CCHX+, and CCX+, analogous to the corresponding hydrogen ions CCHa+, CCH2+, and CCH+. These halogenated ions parallel the behavior of their hydrogen analogs. The cross sections were all less than 1 A2. An example is CCHF+, shown in the insert of Fig. 4. The other fluorine-containing ions, i.e., CCH2F+ and CCF+, were lower in yield than the CCHF+. Similar comments

'Or-----------------------~

CCH+ __ 2

I .1 1 .Q3 1..., ...L---!.....J.......L5...l.....L..L,LlO--1......J20L....L...L..-4L....J...060...l.....L.LJ.J,00

ION ENERGY (eV,cenler of mass)

FIG. 6. Log of cross section versus log projectile on kinetic energy for CCH2+ from (1) CHaF, (2) CHaCl, (3) CHaBr, and (4) CHa!.

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REACTIONS OF C+ IONS 3499

could be made about analogous ions containing the other halogen atoms.

Finally, judging from the compilation in Table I, reactions corresponding to carbanion transfer (CH2-)

to produce C2H2 and HX+ are exothermic, so they might be expected to be observable. Indeed, they were but the yields were small. Their production cross section decreased in the series HX+ as one went from iodine to fluorine. In the latter case no HF+ was actually de­tected but all other HX+ ions were observed.

In the cases of C+ reacting with CH4 I and CHaF 2 a plot of the sum of cross sections for all of the ions observed agreed surprisingly well with the predicted cross section using the Gioumousis and Stevenson (G-S) model.6 If one attempts such a correlation with CHaCl, CHaBr, and CHaI, the results are poor. Our interpretation of this is that in the case of CH4 and CHaF the G-S model, i.e., a point charge, a polarizable sphere and a 1/r4 potential are good approximations. However, as one gets to the higher methyl halides serious deviations from this model arise so that reason­able agreement cannot be expected.

In summary, therefore, it is clear that two important factors influencing the mechanism of the various ion molecule reactions of C+ with CHaX are the polariza­bility of the C-X bond and the energetics of the particular process. To illustrate this we will recall some of the reactions. The X+ ion is produced when a carbanion (CHa-) is picked up by the projectile ion and CHa+ ion production occurs by a corresponding pickup of the halide ion. A plot of cross section versus bond refraction of the C-X bond as given by Denbigh7 is plotted for various processes in Fig. 7. Referring to the production of CHa+, the cross section rises in a linear fashion as the polarizability increases. A similar be­havior, although not plotted in Fig. 7, is observed for the production of X+. In that case, it will be recalled, only I+, Br+, and CI+ were observed. F+ was not observed because of the unfavorable energetics. The three halogen positive ion cross sections fall on a straight line.

An inverse correlation is observed in the case of a neutral fragment pickup reaction. Figure 7 illustrates this situation with the yield of CCH2+ and CCHa+. In these reactions the yield increases with decreasing bond polarizability, and the least polarizable molecule gives highest yield of the ion in question. This is qualitatively reasonable since charged fragment extrac­tion probability decreases as the polarizability decreases, and hence the mechanism for pickup of a neutral fragment becomes more competitive.

The production of CX+ which corresponds to a neutral halogen transfer is an interesting one. At low

3.0~----------------,

2.5

1.5

1.0

.5

4 6 8 10 12 BOND REFRACTION (CC)

14

FIG. 7. Cross sections for the production of various ions versus bond refraction for the C-X bonds.

energies where the experimental evidence supports a stripping mechanism one expects and observes an inverse correlation with polarizability. In the high­energy region where the indication is that the CX+ ions arose from a dissociative mechanism one has the reverse dependence on polarizability.

On the other hand, hydride ion pickup to produce CH2X+ does not show systematic trends in cross section since in the family of molecules, CHaX, the C-H bond polarizability does not change significantly and other factors dominate the course of the reaction.

All of the tabulated figures in Table I, except for the reaction products CF++CHa, were obtained from Franklin et al.s The thermodynamic data for the CF+ reaction was obtained from Hastie et al.9 The heats of formation of the CCHa+ and CCH2+ ions were assumed to be those of the vinyl and acetylene ions, respectively.

* This work was done under the auspices of the U.S. Atomic Energy Commission.

t Present address: Department of Chemistry, Fordham Univer-sity, Bronx, N.Y. .

1 P. S. Wilson, R. W. Rozett, and W. S. KoskI, J. Chern. Phys. 52, 5321 (1970).

2 P. S. Wilson, R. W. Rozett, and W. S. Koski, J. Chern. Phys. 53, 1276 (1970). .

3 E. R. Werner, G. R. Hertel, and W. S. Koski, J. Am. Chern. Soc. 86, 788 (1964).

4 R. W. Rozett and W. S. Koski, J. Chern. Phys. 49, 2691 (1968).

• D. R. Bates, C. J. Cook, and F. J. Smith, Proc. Roy. Soc. (London) 83,49 (1964).

6 G. Gioumousis and D. P. Stevenson, J. Chern. Phys. 29,294 (1958) .

7 K. G. Denbigh, Trans. Faraday Soc. 36,936 (1940). 8 J. L. Franklin, J. G. Dillard, H. M. Rosenstock, J. T. Herron,

K. Drazl, and F. H. Field, Nat!. Std. Ref. Data Ser., Nat!. Bur. Std. (U.S.) 26, (1969).

9 J. W. Hastie and J. L. Margrave, Fluorine Chern. Rev. 2, 77 (1968).

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