Theoretical investigations of the SH and LiS cations

Reliable theoretical data on spectroscopy and spin-orbit matrix elements are computed for the lowest electronic states of SH⁺ and LiS⁺ ions. Accurate spectroscopic predictions for their excited electronic states are given. For SH⁺, polarization minima at large internuclear distances are located in addition to the strongly bound electronic states already known. For LiS⁺, our calculations confirm that the electronic ground state of this ion is of ³Σ⁻ species and reveal the existence of a ¹Δ state presenting a potential well as deep as the potential of the ground state. Moreover, the LiS⁺ electronic excited states potential energy curves possess shallow potential minima in the molecular region and at long-internuclear distances. Generally, these shallow minima may be populated during low energy collisions between the corresponding atomic fragments. Finally, spin-orbit calculations have allowed giving accurate determinations of the spin-orbit splittings for these cations and elucidation of the predissociation mechanisms of SH⁺ leading to the formation of the S⁺ and H species in their electronic ground states. Accordingly, long-lived SH⁺ ions can be found in the X³Σ⁻, a¹Δ and b¹Σ⁺ electronic states and the rovibrational levels of LiS⁺ in its electronically excited and ground states should be weakly perturbed.