MECHANISMS FOR THE HETEROGENEOUS HYDROLYSIS OF HYDROGEN-CHLORIDE, CHLORINE NITRATE AND DINITROGEN PENTOXIDE ON WATER-RICH ATMOSPHERIC PARTICLE SURFACES

The heterogeneous interaction of the stratospheric reservoir species H Cl, ClONO2, and N2O5 with water-rich polar stratospheric particle mimi cs is characterized by the formation of solvated ionic products. Simpl e semiempirical calculations have been used to explain the nature of t he species observed in infrared spectroscopic measurements and to eluc idate the mechanism by which they are formed. The initial stages of th e interaction appear to involve an S(N)2-type nucleophilic attack by t he oxygen atom of the surface water molecule upon the most accessible electrophilic site of the adsorbing reactant. Mechanistic schemes invo lving protonated acid intermediates and their subsequent decomposition or hydrolysis can be used to accurately predict and explain the stabl e reaction products observed spectroscopically under stratospheric con ditions.