Ab initio potential-energy surfaces for the X [sup 2]B[sub 1], Ã [sup 2]A[sub 1], and B [sup 2]B[sub 2] states of the H[sub 2]S[sup +] molecular ion.

Multireference configuration interaction calculations with the cc-pVQZ basis set are reported for the potential-energy surfaces of the &Xtilde;[SUP2] Ã[SUP2] A[SUB1] &Btilde;[SUP2]B[SUB2] 1[SUP4] A[SUB2] and 1[SUP4] B[SUB1] states of H[SUB2]S[SUP+]. Seams of intersection between the states have been characterized and the conical intersection between the Ã[SUP2] A[SUB1] and &Btilde;[SUP2] B[SUB2] states has been located. Optimized geometries and vertical and adiabatic ionization energies are in good agreement with the available experimental data. The &Xtilde;[SUP2] B[SUB1] state is strongly bound with an equilibrium geometry very similar to that of ground-state H[SUB2]S. The equilibrium bond angle for the Ã[SUP2] A[SUB1] state is 126.4°. The dissociation of this state to S[SUP+]([SUP4]S) + H[SUB2] is interpreted in terms of an initial increase in bond angle on formation and a transition to the &Xtilde;[SUP2] B[SUB1] surface at linearity. As the bond angle decreases the intersection with the 1[SUP4] A[SUB2] state is reached and a nonadiabatic transition to this state results in dissociation. It is suggested that the dissociation of the &Btilde;[SUP2] B[SUB2] state to SH[SUP+]([SUP3]∑[SUP-]) + H occurs via asymmetric stretching followed by a nonadiabatic transition to the dissociative 1[SUP4] A'' surface. [ABSTRACT FROM AUTHOR]