The structure, stability, thermochemistry, and bonding in SO3-(H2O)n (n = 1–7) clusters: a computational analysis

Abstract

The structure, stability, and intermolecular interactions in SO3-(H2O)n (n = 1–7) clusters were investigated using density functional and wave functional methods. The putative global minimum shows the SO3 molecule tends to be on the surface water clusters. The increase in the number of water molecules chalcogen bond distance between water molecules and SO3 decreases, while the maximum number of water molecules coordinated to the SO3 molecule remains at three. The calculated solvation energy increases with the increase in the number of water molecules, and it does not saturate, which indicates that the addition of water molecules can add up to the existing water cluster network. The interaction energy between water molecules and SO3 was less than the solvation energy conforming to the cluster forming of water molecules. The Gibbs free energy and entropy values decrease with the increase in cluster size, signifying the amount of water molecule decide the sequential hydration process. Thermochemistry data at various temperatures show that low-temperature regions found in the upper part of the troposphere favor hydration formation. Molecular electrostatic potentials (MESP) show reduced Vs,max value of π-hole on sulfur atom and increased value on hydrogens of water molecules which results in the addition of water which leads to the sequential addition of water molecules to the water network. The quantum theory of atoms in molecules (QTAIM) shows the presence of S···O, O···H interactions between SO3 and water molecules. Between water molecules O···H, H-bonding interactions were observed, and in larger clusters, O···O interaction was also noticed. QTAIM analysis shows that the water–water HBs in these clusters are weak H-bond, while the SO3-water interaction can be classified as medium H-bonds which was further supported by the NCI and 2D RDG plots.