Topography of potential-energy surfaces. Spin–orbit interaction for H + F2, Cl2

Abstract

Potential-energy surfaces have been calculated for the H + F₂ and H + Cl₂ reactions using the DIM (diatomics-in-molecules) method including spin–orbit interaction. The non-adiabatic coupling strength between the two lowest Ω=½ potential-energy surfaces shows two maxima for motion along the minimum-energy pathway. The first maximum occurs early in the exit valley, depends more strongly on H—X bond motion than X—X bond motion and is greatest in the collinear configuration. The second maximum occurs late in the exit valley, depends less on H—X bond motion than on X—X bond motion and is little altered on bending. This bimodal behaviour arises from an energy decrease in the exit valley of the potential-energy surface which is large compared with the spin–orbit interaction.