On the dynamics of exothermic triatomic exchange reactions: Semiclassical model for final state VRT distributions

A semiclassical theory for exothermic exchange reactions is presented which treats the subsystem of translational rotational motion classically and the vibrations quantum-mechanically. The rearrangement of bonds in a given configuration of atoms is described by Franck-Condon-type overlap factors which generalize a recently proposed collinear theory to bent configurations. In order to treat rotational excitation explicitly in a nonstatistical way the classical version of a transformation between reactant and product angular momenta due to a sudden bond exchange is introduced. Additional rotational excitation stems from the release of reaction energy via product repulsion which is taken into account in a simple impulsive model. Calculated product energy distributions P(ν′, j′) show good agreement with experimental and quasiclassical trajectory results for two mass combinations with very different mechanisms of rotational excitation (L+HH→LH+H and H+LL→HL+L). Certain variations of the product energy distribution with the collision energy are reproduced.