Nonadiabatic quantum wave packet dynamics of H+H₂ (HD) reactions

Abstract

Initial state-selected and energy resolved integral reaction cross sections and thermal rate constants of H+H₂ and H+HD reactions are calculated on the conically intersecting ground electronic manifold. The effect of the associated nonadiabatic coupling on these dynamical quantities is examined for energies upto the three-body dissociation limit well beyond the energetic minimum of the seam of conical intersections. The quantum dynamical simulations in the coupled electronic manifold are carried out within the coupled state approximation by a time-dependent wave packet propagation method employing the double many body expansion (DBME) potential energy surface (PES) of Varandas et al. [A.J.C. Varandas, F.B. Brown, C.A. Mead, D.G. Truhlar, N.C. Blais, J. Chem. Phys. 86 (1987) 6258]. All partial wave contributions upto the total angular momentum J=50, in case of H+H₂ and J=60, in case of H+HD reactions are considered to obtain converged reaction cross sections upto a total energy of ∼4.7eV. Channel specific reaction cross sections are reported for the H+HD reaction. Analysis of the reaction probabilities for individual J values reveal no significant effect of nonadiabatic coupling on them at energies above the minimum of the seam of conical intersections occurring at ∼2.74eV. The differences observed in the reaction probability results in the uncoupled and coupled surface situation however, cancel out in the integral reaction cross sections and thermal rate constants. These findings are consistent with the recent studies on these reactions including the geometric phase change.