Ab initio potential-energy surfaces for the X̃ 2B1, Ã 2A1, and B̃ 2B2 states of the H2S+ molecular ion

Abstract

Multireference configuration interaction calculations with the cc-pVQZ basis set are reported for the potential-energy surfaces of the X̃ 2B1, à 2A1, B̃ 2B2, 1 4A2, and 1 4B1 states of H2S+. Seams of intersection between the states have been characterized and the conical intersection between the à 2A1 and B̃ 2B2 states has been located. Optimized geometries and vertical and adiabatic ionization energies are in good agreement with the available experimental data. The X̃ 2B1 state is strongly bound with an equilibrium geometry very similar to that of ground-state H2S. The equilibrium bond angle for the à 2A1 state is 126.4°. The dissociation of this state to S+(4S)+H2 is interpreted in terms of an initial increase in bond angle on formation and a transition to the X̃ 2B1 surface at linearity. As the bond angle decreases the intersection with the 1 4A2 state is reached and a nonadiabatic transition to this state results in dissociation. It is suggested that the dissociation of the B̃ 2B2 state to SH+(3∑−)+H occurs via asymmetric stretching followed by a nonadiabatic transition to the dissociative 1 4A″ surface.