Hydration of OCS with One to Four Water Molecules in Atmospheric and Laboratory Conditions

Carbonyl sulfide is the most abundant sulfur gas in the atmosphere. We have used MP2 and CCSD(T) theory to study the structures and thermochemistries of carbonyl sulfide interacting with one to four water molecules. We have completed an extensive search for clusters of OCS(H2O)n, where n = 1−4. We located three dimers, two trimers, five tetramers, and four pentamers with the MP2/aug-cc-pVDZ method. In each of the complexes with two or more waters, OCS preferentially interacts with low-energy water clusters. Our results match current theoretical and experimental literature, showing correlation with available geometries and frequencies for the OCS(H2O) species. The CCSD(T)/aug-cc-pVTZ thermochemical values combined with the average amount of OCS and the saturated concentration of H2O in the troposphere, lead to the prediction of 106 OCS(H2O) clusters·cm−3 and 102 OCS(H2O)2 clusters·cm−3 at 298 K. We predict the structures of OCS(H2O)n, n = 1−4 that should predominate in a low-temperature molecular beam and identify specific infrared vibrations that can be used to identify these different clusters.