Quasiclassical state to state reaction cross sections for D+H 2(v=0, j=0)→HD(v′,j′)+H. Formation and characteristics of short-lived collision complexes

Abstract

State resolved total and differential reaction cross sections, as well as reaction probabilities, have been calculated by the quasiclassical trajectory (QCT) method for the D+H2(v=0, j=0)→HD(v′,j′)+H reaction on the Liu-Siegbahn-Truhlar-Horowitz potential energy surface in the collision energy range 0.30-1.25 eV. Thus a detailed comparison with existing fully converged quantum mechanical (QM) calculations has been performed. The general agreement between both sets of results is good with some differences. QCT integral reaction cross sections for the production of HD(v′=0) are lower than the corresponding QM ones by 10%-15% for collision energies higher than 0.6 eV, and the energy dependence of the QCT reaction probability with a total angular momentum J equal to zero shows no structure when summed over all j′ states (contrary to the QM case). The differential cross sections for the lowest j′ values show, when represented as a function of energy, a "ridge" feature similar to the one found in exact QM calculations and attributed to a broad resonance. The analysis of the trajectories leading to low j′ shows progressively longer collision times as the scattering angle decreases. The longest-lived trajectories, related to the formation of short-lived complexes, cause local maxima in the differential cross section at the lowest scattering angles for each energy. These local maxima are the origin of the ridge. The lifetime of the classical short-lived complexes is estimated to be 15-35 fs, clearly larger than the lifetimes obtained from the width of the ridge feature, when interpreted as a quantum mechanical resonance. © 1992 American Institute of Physics.