Adsorption of Some Atmospherically Important Molecules onto Large Water Clusters: SO2, SO3, HCl, and ClONO2

Abstract

AbstractThe adsorption of a range of atmospherically important molecules (SO2, SO3, HCl, and ClONO2) on large water clusters have been studied using a supersonic molecular beam expansion to generate water clusters containing 50–450 water molecules. SO2 and HCl were found to stick with low efficiency to the water cluster, retaining their chemical identity. In contrast, both SO3 and ClONO2 undergo heterogeneous reactions on the surface of the water cluster forming, respectively, H2SO4 and HOCl with HNO3. For SO3, calculations show that the large barrier that exists in the gas‐phase to the reaction of SO3 with water is removed for water clusters of a sufficient size because of stabilization of the transition state by solvation. For ClONO2, the barrier to reaction is much larger and cannot be removed by solvation for any size cluster. In this case, it is likely that reaction takes place on the water cluster by the ionic dissociation of ClONO2 in a similar manner to that observed for ClONO2 on ice films.