On the products’ translational distribution for the reactions of CH3I and CF3I with K and Ba

Abstract

A reanalysis is presented of the available literature data on the recoil velocity distribution of the KI product in the crossed beam reaction of K with CH3I (and with CF3I) and the resulting recoil distribution function P (Etr′) of final relative translational energy E′tr. For the CF3I reaction (at an average initial translational energy ?tr=2.9 kcal mol−1) the average c.m. recoil energy ?′tr is 7.6 kcal mol−1, corresponding to only 27% conversion of the total available energy E into product translation, compared to a value of 57% for the CH3I reaction (of about the same E, at the same ?tr). The probability density function for the KI velocity (i.e., linear momentum) in the backward (’’rebounding’’) direction is essentially Gaussian. These data are used as a test of several distinguishable impulsive models, e.g., those of Herschbach and of Levine et al. The results for the alkali reactions are compared to those of the analogous Ba reactions; qualitative differences are noted. Much of the apparent diversity can be readily understood in terms of the unifying variable p′, the products’ recoil momentum. The most probable value of p′ is not very different for all the reactions considered, in accord with the so-called photodissociation model of Herschbach and Harris. The near-Gaussian shapes of the recoil momentum distributions are in qualitative accord with the information-theoretic form of Levine et al.