Theoretical studies of heterogeneous reaction mechanisms relevant for stratospheric ozone depletion

Aspects of the heterogeneous reaction HCl + ClONO2 + Cl-2 + HNO3 on ice and N2O5 + H2O --> 2 HNO3 on supercooled water are modeled via electronic-stru cture calculations involving reactant-water cluster systems. Reaction-path calculations for a HCl . ClONO2 (H2O)(9) system indicate a coupled proton-t ransfer (PT)/nucleophilic attack (S(N)2) process, in which the ice lattice is an active participant. Analysis of the N2O5.(H2O)(4) reaction system geo metry and charge distribution suggests that a similar coupled PT/S(N)2 mech anism could occur in a larger system. (C) 1999 John Wiley & Sons, Inc.