How Flexible Is the Hydrogen Sulfide Molecule Structure? Influence of Hydrogen Sulfide Molecule Geometry on Its Hydrogen Bonds.

The geometry of hydrogen sulfide was studied by calculating potential energy surface (PES) with over 1800 configurations. The calculations were performed at very accurate CCSD(T)/aug-cc-pvz5 level. The most stable geometry on the PES has bond angle (H-S-H) of 92.40° and bond length (S-H) of 1.338 Å. The PES shows that hydrogen sulfide is a quite flexible molecule. Namely, it can change the bonding angle (H-S-H) in the range of 15.6° (from 84.6° to 100.2°) and the bond lengths (S-H) in the range of 0.082 Å (from 1.299 Å to 1.381 Å) with an energy increase of only 1.0 kcal/mol. An influence of hydrogen sulfide geometry on its hydrogen bonds was studied on several hydrogen sulfide/hydrogen sulfide and water/hydrogen sulfide dimers. It showed that the change of hydrogen sulfide geometry does not influence the strength of hydrogen bond. Fully optimized geometries in gas and water solution phases revealed structural differences of both monomers and dimers in gas phase and water phase. SAPT analysis of the optimized dimer geometries showed that in all the dimers electrostatic is the most dominant contribution, while, in the dimers with hydrogen sulfide, the influence of dispersion contribution becomes quite pronounced.