Examination of the Structures, Energetics, and Vibrational Frequencies of Small Sulfur-Containing Prototypical Dimers, (H2S)2 and H2O/H2S

The optimized geometries, vibrational frequencies, and dissociation energies from MP2 and CCSD(T) computations with large correlation consistent basis sets are reported for (H2S)(2) and H2O/H2S. 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 H2O/H2S 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 center dot center dot center dot SH2 configuration (H2O donor) lies only 0.2 kcal mol(-1) below the HSH center dot center dot center dot OH2 structure (H2S 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). (C) 2018 Wiley Periodicals, Inc.