Heats of formation of the H1,2OmSn (m, n = 0-3) molecules from electronic structure calculations

Atomization energies at 0 K and heats of formation at 0 and 298 K are predicted from high level ab initio electronic structure calculations using the coupled cluster CCSD(T) method with augmented correlation-consistent basis sets extrapolated to the complete basis set (CBS) limit for the H(1,2)O(m)S(n) (m, n = 0-3) compounds, as well as various radicals involved in different bond breaking processes. To achieve near chemical accuracy (+/-1.0 kcal/mol), additional corrections were added to the CBS binding energies based on the frozen core CCSD(T) energies including corrections for core-valence, scalar relativistic, and first-order atomic spin-orbit effects. Geometries were optimized up through the CCSD(T)/aV(T+d)Z level. Vibrational zero point energies were computed at the MP2/aV(T+d)Z level. The calculated heats of formation are in excellent agreement with the available experimental data and allow the prediction of adiabatic bond dissociation energies (BDEs) to within +/-1.0 kcal/mol. The decomposition mechanisms were largely determined by a preference to maintain a strong S=O bond in the dissociated products as opposed to O=O and S=S bonds, exactly matching the ordering of the BDEs in the diatomics. For the H(2)X(2) and H(2)X(3) systems, as well as the HX(3) radicals, the energetically favorable decomposition pathway leads to the formation of XH radicals and breaking the X-X bond as opposed to breaking the X-H bond. For the HX(2) radicals, however, the more thermodynamically favorable pathway leads to a breaking of the H-X bond and forming X(2) molecules.