Double many-body expansion potential energy surface for ground state HSO2.

A global potential energy surface is reported for the ground electronic state of HSO2 by using the double many-body expansion (DMBE) method. It employs realistic DMBE functions previously reported from accurate ab initio calculations (in some cases, fine tuned to spectroscopic data) for the triatomic fragments, and four-body energy terms that were modelled by fitting novel ab initio FVCAS/AVTZ calculations for the tetratomic system. In some cases, FVCAS/AVDZ energies have been employed after being scaled to FVCAS/AVTZ ones. To assess the role of the dynamical correlation, exploratory single-point Rayleigh-Schrödinger perturbation calculations have also been conducted at one stationary point. All reported calculations are compared with previous ab initio results for the title system. The potential energy surface predicts HOSO to be the most stable configuration, in good agreement with other theoretical data available in the literature. In turn, the HSO2 isomer with H bonded to S is described as a local minimum, which is stable with respect to the H + SO2 dissociation asymptote.