Evidence for Interfacial [FDCl]⁻ in Collisions between DCl and F⁻ in KF−Glycerol Solutions

Abstract

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 F − ions 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. F − ions eliminate rapid DCl → HCl exchange at concentrations of 2.5 and 4.0 M KF, instead converting DCl into HF molecules that slowly desorb from solution. F − ions also steal away thermalized DCl molecules that would have desorbed from the surface of pure glycerol. This scavenging of DCl by F − implies that some F − ions approach DCl molecules near the surface and form [FDCl] − . The complex then decays into DF and Cl −, followed by DF → HF exchange and slow HF evaporation. Among the halide ions investigated, only F − suppresses near interfacial DCl → HCl exchange and DCl desorption whereas I − and Br − enhance these processes. The F − ion, however, appears to be more effective than I −: in a mixture of 1.6 M KI and 1.6 M KF, I − ions only slightly inhibit scavenging of DCl by F − .