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 center dot center dot center dot O and O center dot center dot center dot 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 pi-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 center dot center dot center dot O, O center dot center dot center dot 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 center dot center dot center dot O, O center dot center dot center dot O chalcogen bonds in addition to the hydrogen bonds. [GRAPHICS] .