Selected ion flow tube study of the reactions between gas phase cations and CHC12F, CHC1F2 and CH2C1F

Christopher Howle, Christopher Mayhew, Richard Tuckett

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The branching ratios and rate coefficients have been measured at 298 K for the reactions between CHCl\(_2\)F, CHClF\(_2\) and CH\(_2\)ClF and the following cations (with recombination energies in the range 6.3 - 21.6 eV); H\(_3\)O\(^+\), SF\(_x\)\(^+\) (x = 1 - 5), CF\(_y\)\(^+\) (y = 1  3), NO\(^+\), NO\(_2\)\(^+\), O\(_2\)\(^+\), Xe\(^+\), N\(_2\)O\(^+\), O\(^+\), CO\(_2\)\(^+\), Kr\(^+\), CO\(^+\), N\(^+\), N\(_2\)\(^+\), Ar\(^+\), F\(^+\) and Ne\(^+\). The majority of the reactions proceed at the calculated collisional rate, but the reagent ions SF\(_3\)\(^+\), NO\(^+\), NO\(_2\)\(^+\) and SF\(_2\)\(^+\) do not react. Surprisingly, although all of the observed product channels are calculated to be endothermic, H\(_3\)O\(^+\) does react with CHCl\(_2\)F. On thermochemical grounds, Xe\(^+\) appears to react with these molecules only when it is in its higher-energy \(^2\)P\(_{1/2}\) spin-orbit state. In general, most of the reactions form products by dissociative charge transfer, but some of the reactions of CH\(_2\)ClF with the lower-energy cations produce the parent cation in significant abundance. The branching ratios produced in this study and by threshold photoelectron-photoion coincidence spectroscopy (preceding paper) agree reasonably well over the energy range 11 - 22 eV. In about one fifth of the large number of reactions studied the branching ratios are in excellent agreement and appreciable energy resonance between an excited state and the ground state of the ionized neutral exists, suggesting that these reactions proceed exclusively by a long-range charge transfer mechanism. Upper limits for the enthalpy of formation at 298 K of SF\(_4\)Cl (-637 kJ mol\(^{-1}\)), SClF (-28 kJ mol\(^{-1}\)) and SHF (-7 kJ mol\(^{-1}\)) are determined.
Original languageEnglish
Pages (from-to)3626-3636
Number of pages11
JournalThe Journal of Physical Chemistry A
Issue number16
Publication statusPublished - 2 Apr 2005


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