Reactive scattering dynamics on conically intersecting potential energy surfaces: The H+H-2 exchange reaction

We investigate the dynamics of a bimolecular reaction on conically intersec ting potential energy surfaces. The flux operator method of calculating the state-specific total reaction probability is extended to a coupled-surface problem, both in the diabatic and adiabatic electronic representations. Th e reaction probabilities are calculated from their expectation values with the aid of a time-dependent wave packet (WP) approach. The initial WP is pr epared in an adiabatic electronic state, and it is propagated in a suitable diabatic electronic representation The initial state-specific and energy-r esolved reaction probability is given in analytical forms in both the adiab atic and diabatic picture. The diagonal correction (Born-Huang term) to the uncoupled adiabatic (Born-Oppenheimer) Hamiltonian is discussed. The above formalism is applied to the H + H-2 exchange reaction on its conically int ersecting double many-body expansion (DMBE) potential energy surfaces. We r eport the initial state-selected reaction probabilities for energies extend ing up to the onset of the three-body dissociation of this system, We find only a minor impact of the conical intersection on the reactive scattering dynamics of H + H-2. A closer inspection of the electronic population revea ls a very small fraction of the WP traversing the upper adiabatic sheet dur ing the course of the reaction. The accuracy of the DMBE potential energy s urface is assessed by comparing with new ab initio data.