A time-dependent wave packet study of the vibronic and spin-orbit interactions in the dynamics of $Cl(2P)+H2→HCl(X̃ 1Σg+)+H(2S)$ reaction

We investigate the vibronic and spin-orbit (SO) coupling effects in the state-selected dynamics of the title reaction with the aid of a time-dependent wave packet approach. The ab initio potential energy surfaces of Capecchi and Werner [Science 296, 715 (2002)] have been employed for this purpose. Collinear approach of the $Cl(2P)$ atom to the $H2$ molecule splits the degeneracy of the $P2$ state and gives rise to $Σ2$ and $Π2$ electronic states. These two surfaces form a conical intersection at this geometry. These states transform as $1 2A′,$ $1 2A″,$ and $2 2A′,$ respectively, at the nonlinear configurations of the nuclei. In addition, the SO interaction due to Cl atom further splits these states into ²Σ_1/2, ²Π_3/2, and ²Π_1/2 components at the linear geometry. The ground-state reagent $Cl(2P3/2)+H2$ correlates with ²Σ_1/2 and ²Π_3/2, where as the SO excited reagent $Cl*(2P1/2)+H2$ correlates with ²Π_1/2 at the linear geometry. In order to elucidate the impact of the vibronic and SO coupling effects on the initial state-selected reactivity of these electronic states we carry out quantum scattering calculations based on a flux operator formalism and a time-dependent wave packet approach. In this work, total reaction probabilities and the time dependence of electronic population of the system by initiating the reaction on each of the above electronic states are presented. The role of conical intersection alone on the reaction dynamics is investigated with a coupled two-state model and for the total angular momentum $J=0$ (neglecting the electronic orbital angular momentum) both in a diabatic as well as in the adiabatic electronic representation. The SO interaction is then included and the dynamics is studied with a coupled three-state model comprising six diabatic surfaces for the total angular momentum $J=0.5$ neglecting the Coriolis Coupling terms of the Hamiltonian. Companion calculations are carried out for the uncoupled adiabatic and diabatic surfaces in order to explicitly reveal the impact of two different surface coupling mechanisms in the dynamics of this prototypical reaction.