Quasi-classical treatment of the Stereodynamics of chemical reactions: k-r-k ' vector correlation for the Li+HF(v=1,j=1)-> LiF+H reaction

We present a classical treatment of the k-r-k' vector correlation for atom- diatom reactions, involving the directions of the initial and final relativ e velocities and the internuclear axis of the diatom. The formalism is base d on the expansion of the joint probability distributions in multipolar mom ents, and it is analogous to that developed for the vector correlations imp lying the initial or final rotational angular momentum. Within the framewor k of classical mechanics, the present treatment allows the determination of the differential cross section for any preparation of the internuclear axi s and for any initial rotational angular momentum of the reactants. This me thodology has been applied to the study of the steric effect in the Li+HF(v = 1,j = 1,m = 0)-->LiF+H reaction and the theoretical results have been co mpared via simulation with the recent experimental determination by Loesch and co-workers of laboratory angular distributions (LAB ADs) for several di stributions of the internuclear axis of HF. Very good agreement has been fo und between experimental and simulated LAB AD, allowing an interpretation o f the experimental results. Although the integral steric effect is very sma ll, the differential and/or state resolved steric effects are more pronounc ed. Moreover, it has been found that by varying the preparation of the inte rnuclear axis of the HF molecule, the population of final states of the LiF changes noticeably, which represents a clear case of control of the outcom e of a chemical reaction. (C) 2001 American Institute of Physics.