Effect of water molecule in the structure, stability, and electronic properties of sulfur trioxide clusters: a computational analysis

The structure and stability of SO₃ and hydrated SO₃ clusters are examined using density functional theory calculations. The nature of interactions is explored by quantitative molecular electrostatic potential (MESP), atoms in molecules (AIM), and energy decomposition analysis (EDA). The most stable isomers of SO₃ clusters are formed by the dominant intermolecular S···O and O···O chalcogen bonding. In hydrated SO₃ clusters, a maximum number of three hydrogen bonds occurs between water and SO₃ molecules. The binding energies were all negative and increase monotonically, while the cluster adsorption energy increases with the sulfur trioxide cluster size, and reaches a saturation. The thermodynamic parameters for the formation of hydrated sulfur trioxide clusters show a large entropy contribution and the reaction is enthalpy driven. MESP analysis shows that the π-hole values on the SO₃ molecules at the outer surface have larger values than the free SO₃ molecule which helps the clusters to grow. In the hydrated SO₃ clusters up to heterotetramer, the strengthening of positive potential on hydrogen atoms attracts the new SO₃ molecules. The QTAIM analysis shows the presence of S···O, O···O intermolecular chalcogen bondings. The EDA result shows that electrostatic attraction is dominant, while orbital interaction increases with the cluster size in hydrated SO₃ clusters. A comparative examination of energetical parameters of hydrated SO₂ with hydrated SO₃ clusters shows the latter to have less binding energy and high cluster adsorption energy supporting its higher reactivity and the formed species is stabilized by S···O, O···O chalcogen bonds in addition to the hydrogen bonds. Graphical abstract: [Figure not available: see fulltext.]