Hydrogen Bond Interaction Networks in the Mixed Pentamers of Hydrogen Sulfide and Water

The observation of gas-phase water clusters has been instrumental in understanding water aggregation and cooperativity, paving the way for solvation models in the bulk. However, the characterization of hydrogen sulfide self-aggregation is still largely unexplored. Here, we investigate two mixed pentamers of hydrogen sulfide and water to examine the influence of the weaker, dispersion-based and less directional interactions caused by hydrogen sulfide. Unprecedented structural resolution was obtained by combination of jet-cooled broadband rotational spectroscopy and quantum-chemical calculations. Specifically, we compare the 4:1 and 1:4 hydrogen sulfide - water pentamers, offering comparison with the prototype homoclusters. Important structural differences are revealed in the hydrogen sulfide clusters, which reorganize to compensate for the weaker sulfur-centered hydrogen bonds. The noncovalent interactions in the pentamers were rationalized using density functional theory and reduced electronic density calculations. Moreover, a comprehensive many-body decomposition energy analysis revealed significant variations in molecule two- and three-body contributions to the total interaction energy based on the relative proportions of H₂O and H₂S. These findings offer new insights into the distinct cooperative forces in water and hydrogen sulfide clusters. The results will improve our understanding and modeling of sulfur-centered hydrogen bonds, which may be useful across various research fields, including protein folding, molecular aggregation, materials science, and computational benchmarking.