Mixed H₂S and H₂O Clusters─New Insights into Dispersion-Dominated Hydrogen Bonding

Here, we report the results of an IR spectroscopy study on heteroclusters of H₂S and H₂O and several of their isotopomers using mass-selective IR spectroscopy in superfluid helium nanodroplets in the range of 2560-2800 cm^-1. Based on DFT calculations on the B3LYP-D3/6-311++G(d,p) level of theory, we were able to assign the experimentally observed O-D stretching bands to heterodimer and heterotrimer clusters. Since no bands of the S-H-bound conformer HSH···OH₂ could be observed, we were able to determine the O-H-bound conformer HOH···SH₂ to be the global minimum structure. A trapping of the local minima in helium nanodroplets was not observed. This is in line with the weaker hydrogen bond expected for H₂S complexes. In these clusters, the interaction energy is expected to be more dominated by dispersion and less dictated by highly directional electrostatic forces.