High-accuracy coupled-cluster computations of bond dissociation energies in SH, H2S, and H2O

Abstract

The first and second bond dissociation enthalpies of H2S have been investigated at up to the CCSD(T)/aug-ccpV6Z level of theory. Corrections for core/valence electron correlation, anharmonic zero point vibrational energy and relativistic effects were followed by extrapolation to the complete basis set limit. Analysis of direct dissociation yields D0(S–H)=349.9 and D0(HS–H)=375.8 kJ mol−1. Together these imply an atomization enthalpy for H2S about 1 kJ mol−1 larger than literature evaluations. Consideration of exchange of a second H atom from OH to SH yields D0(HS–H)=376.2 kJ mol−1. The two computations of D0(HS–H) lie within 0.5 kJ mol−1 of a recent spectroscopic measurement of D0(HS–H)=376.24±0.05 kJ mol−1 [R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, J. Phys. Chem. A 104, 4339 (2000)]. The deuterated analogs SD and D2S are also considered. There is also accord to within 1.5 kJ mol−1 with D0(S–H)=348.4±0.8 kJ mol−1, which we derive from the experimental literature. We propose revised enthalpies of formation, ΔfH0(2Π3/2SH)=142.6±0.8 kJ mol−1 and ΔfH298.15(SH)=143.1±0.8 kJ mol−1. The results suggest the dominant uncertainties in these high-level calculations come from the basis set extrapolation and scalar relativistic terms, and that both contribute about 1 kJ mol−1 uncertainty. We also obtain D0(H–OH)=492.6 kJ mol−1, which compares well with recent experiments.