9098 J. Phys. Chem. B 1997,101, 9098-9106

John R. Morris Peter M. Behr, Melissa D. Antman, Bradley R. Ringeisen, Jennifer Splan, *and Gilbert M.*

Department of Chemistry, University of Wisconsin, 1101 University Ave., Madison, Wisconsin 53706-1322

Proton exchange, residence time, and gas uptake measurements are used to explore collisions and reactions of HCl, HBr, and HNO3 with 70 wt % D2SO4 at 213 K. These studies help to provide a detailed picture of HX (X = Cl, Br, NO3) energy transfer to sulfuric acid and the fate of the HX molecules immediately after they thermalize at the D2O/D2SO4 surface. We find that the three molecules readily dissipate their excess kinetic energy and become trapped momentarily in the interfacial region. However, only 11 ± 3% of the thermalized HCl and 22 ± 3% of the thermalized HBr molecules undergo HÆD exchange; the HCl and HBr that do not react are found to desorb from the acid within 2x10-6 s. In contrast, greater than 95% of the initially trapped HNO3 molecules are converted to DNO3. The HX molecules that undergo exchange dissolve within the deuterated acid for characteristic times of 5x10-5 s (HCl), 3x10-3 s (HBr), and 1x10-1 s (HNO3) before they desorb thermally as DX. The scattering experiments imply that the desorption of thermalized HCl and HBr molecules is on average faster than their solvation and reaction in the interfacial and bulk regions of 70 wt % D2SO4. Although HNO3 is less acidic than HCl or HBr, it appears to hydrogen bond more strongly to surface D2O and D2SO4, enabling it to be captured by the acid in nearly every collision.