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

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 D-0(S-H)=349.9 and D-0(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 D-0(HS-H)=376.2 kJ mol(-1). The two computations of D-0(HS-H) lie within 0.5 kJ mol-1 of a recent spectroscopic measurement of D-0(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 D-0(S-H)=348.4+/-0.8 kJ mol(-1), which we derive from the experimental literature. We propose revised enthalpies of formation, Delta(f)H(0)((2)Pi(3/2)SH)=142.6+/-0.8 kJ mol(-1) and Delta(f)H(298.15)(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 D-0(H-OH)=492.6 kJ mol(-1), which compares well with recent experiments. (C) 2002 American Institute of Physics.