Accurate ab initio double many-body expansion potential energy surface for ground-state H2S by extrapolation to the complete basis set limit

A single-sheeted potential energy surface is reported for the electronic ground-state of H2S by fitting accurate multireference configuration interaction energies calculated using aug-cc-pVTZ and aug-cc-pVQZ basis sets with extrapolation of the electron correlation energy to the complete basis set limit, plus extrapolation to the complete basis set limit of the complete-active-space self-consistent field energy. A switching function formalism has been used to warrant the correct behavior at the H-2(X (1)Sigma(+)(g))+S(D-1) and SH(X (2)Pi)+H(S-2) dissociation limits. The topographical features of the novel global potential energy surface are examined in detail, with the former being used for exploratory quasiclassical trajectory calculations of the thermal rate constant for the S(D-1)+H-2, S(D-1)+D-2, and S(D-1)+HD reactions at room temperature. A comparison with other available potential energy surfaces as well as kinetics data is also provided.