The fate of DCl molecules striking pure glycerol and a 2.6 M NaI-glycerol solution is investigated using scattering, uptake, and residence time measurements. We find that dissolved Na+ and I- ions alter every gas-liquid pathway from the moment of contact of DCl with the surface to its eventual emergence as HCl. In particular, the salt enhances both trapping-desorption of DCl and interfacial DCl --> HCl exchange at the expense of DCl entry into the bulk solution. The reduced entry and enhanced desorption of thermalized DCl molecules are interpreted by assuming that Na+ and I- ions bind to interfacial OH groups and tie up surface sites that would otherwise capture incoming DCl molecules. These ion-glycerol interactions may also be responsible for enhancing interfacial D --> H exchange by disrupting the interfacial hydrogen bond network that carries the newly formed H+ ion away from its Cl- pair. This disruption may increase the fraction of interfacial Cl- and H+ that recombine and desorb immediately as HCl before the ions separate and diffuse deeply into the bulk.

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 f HCl exchange, and longtime solvation and dissociation. The electrolytes NaI and CaI 2 enhance immediate DCl desorption and D f 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 f 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.

Fluoride ions dissolved in glycerol readily react with DCl molecules from the gas phase when they come into contact in the near-interfacial region. These reactions are investigated by directing DCl molecules at the surface of 0.5-4.0 M KF-glycerol solutions in vacuum and monitoring the velocities and residence times of the DCl, HCl, and HF products. Although Fions are expected to be repelled from the surface region, we find that they radically alter two near-interfacial channels: the submicrosecond conversion of DCl into HCl and desorption of intact DCl. Fions eliminate rapid DCl f HCl exchange at concentrations of 2.5 and 4.0 M KF, instead converting DCl into HF molecules that slowly desorb from solution. Fions also steal away thermalized DCl molecules that would have desorbed from the surface of pure glycerol. This scavenging of DCl by Fimplies that some Fions approach DCl molecules near the surface and form [FDCl] -. The complex then decays into DF and Cl -, followed by DF f HF exchange and slow HF evaporation. Among the halide ions investigated, only Fsuppresses near interfacial DCl f HCl exchange and DCl desorption whereas Iand Brenhance these processes. The Fion, however, appears to be more effective than I -: in a mixture of 1.6 M KI and 1.6 M KF, Iions only slightly inhibit scavenging of DCl by F -.