The Roles of Salt Concentration and Cation Charge in Collisions of Ar and DCl with Salty Glycerol Solutions of NaI and CaI₂

Abstract

Gas−liquid scattering experiments are used to investigate the roles of ion concentration and ion charge in reactions of DCl with glycerol containing dissolved NaI and CaI 2 . Previous studies show that DCl molecules follow one of three pathways upon adsorption at the surface of pure glycerol: immediate desorption of DCl back into the gas phase, near-interfacial DCl → HCl exchange, and longtime solvation and dissociation. The electrolytes NaI and CaI 2 enhance immediate DCl desorption and D → H exchange at the expense of bulk solvation. We find that these enhancements rise linearly from 1.2 to 3.9 M NaI (5.5 to 1.4 glycerol molecules per ion), suggesting that the limited solvation of Na + and I - and greater ion−ion association at higher concentrations do not abruptly change or reverse trends in these pathways. DCl desorption and D → H exchange are equally enhanced by 0.7 M CaI 2 and 1.2 M NaI (nearly equal I - concentrations), but 1.3 M CaI 2 is twice as effective as 2.6 M NaI. This departure may be driven by the closer proximity of Ca 2+ to the surface at higher ion concentrations, especially if ion pairing between Ca 2+ and surface-active I - drags the cation toward the interfacial region. Argon atom scattering and surface tension measurements provide independent evidence for the presence of ions at the surfaces of the salt solutions.