Translational energy requirements and disposal in molecular collisions. I. Cross sections and probability matrices for the alkali atom-alkyl iodide reactions

H. Kaplan*, R. D. Levine

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

28 Scopus citations

Abstract

A general method of the prediction of the role of translational energy in molecular collisions is introduced and applied. The method is based on an information theoretic construction of a probability matrix subject to microscopic reversibility and to additional dynamic constraints. Applications to the exchange reaction of an alkali atom with an alkyl iodide are extensively considered. Particular attention is given to the translational energy dependence of the reaction cross section, to the influence of reagent internal excitation on the reactivity and to the systematics of the translational energy disposal. The predictions here presented are based on the assumption that the collision dynamics are governed primarily by the transfer of momentum constraint. The Lagrange parameters are then determined either from the measured energy disposal or from a simple model. It is thus possible to predict the translational energy dependence of the reaction cross section (or other dynamical aspects) knowing only the translational energy disposal in reactive collisions. The major predictions are that, at low energies, reagent internal excitation is more effective than translational in causing reaction and that the exoergicity is preferentially released as internal excitation. However, when there is a significant change in the reduced mass during the reaction (2μf < μi) a role reversal occurs at higher energies. Reagent translation enhances the reactivity and energy is preferentially released into product translation. An efficient conversion of reagent internal excitation into translation (or vice versa) is also found in 'super-inelastic' collisions. Such non-reactive collisions are shown to be potentially possible when the corresponding reactive collision satisfies the 2μf < μi criterion.

Original languageEnglish
Pages (from-to)103-123
Number of pages21
JournalChemical Physics
Volume18
Issue number1-2
DOIs
StatePublished - 1 Dec 1976

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