Ab initio calculations of some weakly bound dimers and complexes: II. The complexes of carbon dioxide with water and hydrogen sulphide

The properties of the complex formed between carbon dioxide and water have been studied at the level of second-order Møller-Plesset perturbation theory, using two medium-sized basis sets, 6-31++G(d,p) and 6-311++G(d,p), and a larger basis set, aug-cc-pVTZ. We have examined a number of plausible starting structures, and our calculations have converged on what we believe is the true structure of this aggregate. In order to give additional credibility to our findings, we have extended the calculations to include the analogous complex of carbon dioxide with hydrogen sulphide, using the same combinations of theory and basis set, in order to explore the effect of substituting sulphur for oxygen, either in an SH…O versus an OH…O hydrogen-bonded adduct, or as the site of electron donation in a C…S versus a C…O electron donor-acceptor interaction. We find that, for the same basis set, the most probable structures of both complexes are qualitatively similar, and we report the predicted structures, interaction energies and vibrational spectra of the complexes H2O·CO2 and H2S·CO2 and comment on the similarities and differences between their properties.