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 HO and HS. 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.