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Water and hydrogen sulfide will bind with every atomic cation from the first three rows of the periodic table. While some atoms bind more tightly than others, explicitly correlated coupled cluster theory computations show that energy is required to be put into the system in order to dissociate these bonds even for noble gas atoms. The most promising systems have shallow entrance potential energy surfaces (PESs) that lie above deeper wells of a different spin. These wells are shown explicitly for H 2 OO + , H 2 SS + , and H 2 OS + where relaxed PESs of the heavy atom bond lengths indicate that quartet states will cross more deeply-bound doublet states allowing for relatively easy association but much more difficult dissociation. In astrophysical regions that are cold and diffuse, such associations could lead to the formation of novel molecules utilizing water (or H 2 S) as the building blocks of more rich subsequent chemistry. Recent work has hypothesized that oxywater (H 2 OO) may be an intermediate in the formation of molecular oxygen in comets, and this work supports such a conclusion at least from a molecular cation perspective. 

The optimized geometries, vibrational frequencies, and dissociation energies from MP2 and CCSD(T) computations with large correlation consistent basis sets are reported for (H₂S)₂and 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⋯SH₂configuration (H₂O donor) lies only 0.2 kcal mol⁻¹below the HSH⋯OH₂structure (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. © 2018 Wiley Periodicals, Inc.