Examination of the structures, energetics, and vibrational frequencies of small sulfur-containing prototypical dimers, (H2 S)2 and H2 O/H2 S.

The optimized geometries, vibrational frequencies, and dissociation energies from MP2 and CCSD(T) computations with large correlation consistent basis sets are reported for (H2 S)2 and H2 O/H2 S. Anharmonic vibrational frequencies have also been computed with second-order vibrational perturbation theory (VPT2). As such, the fundamental frequencies, overtones, and combination bands reported in this study should also provide a useful road map for future spectroscopic studies of the simple but important heterogeneous H2 O/H2 S dimer in which the hydrogen bond donor and acceptor can interchange, leading to two unique minima with very similar energies. Near the CCSD(T) complete basis set limit, the HOH⋯SH2 configuration (H2 O donor) lies only 0.2 kcal mol-1 below the HSH⋯OH2 structure (H2 S donor). When the zero-point vibrational energy is included, however, the latter configuration becomes slightly lower in energy than the former by <0.1 kcal mol-1 . © 2018 Wiley Periodicals, Inc.