Theoretical study of the MgSH radical

Abstract

Ab initio RCCSD(T) and MRCI calculations have been carried out for the ground and excited electronic states of MgSH. For the X 2A′ state a quartic force field has been generated using the RCCSD(T) approach and spectroscopic constants for MgSH and MgSD have been obtained from standard second order perturbation theory. The bent equilibrium geometry is found to be in a reasonably good agreement with previous empirical values. The anharmonic fundamental wavenumbers (in cm −1) are calculated to be 408 (MgS stretch), 470 (bending) and 2572 (SH stretch) for MgSH, whereas the lowest frequency in MgSD at 330 corresponds to the bending, the MgS stretch is calculated to lie at 421 and the SD stretch at 1867 (all values are in cm −1). For the low-lying doublet and quartet excited states the Mg⋯SH and MgS⋯H colinear paths to dissociation asymptotes are calculated and several regions of conical intersections are located. It is found that the first two 2Π lead to bent/bent Renner–Teller pairs, but their 2A′ components form a conical intersection for an apex angle around 140°. Hence all four resulting electronic components are rovibronically coupled. As in other alkaline-earth monohydrosulfide the future experimental electronic spectra between the ground and A, B and C doublet states, calculated to lie at 23000–26000 cm −1, could provide additional information about this radical.