Ab initio calculations of the catalytic impact of H2SO4 and HSO4- on the reaction of HCl with ClNO3

The reaction of chlorine nitrate with hydrogen chloride catalysed by sulfuric acid molecules and by the hydrogen sulfate anion has been investigated by means of ab initio calculations at Hartree-Fock and MP2 levels of theory. Geometries of reactants, products and transition states have been optimized using 6-31G*** and 6-31 + + G(2D,2P) basis sets. While the reaction barrier of the gas phase reaction does not decrease significantly with sulfuric acid, it vanishes completely if the hydrogen sulfate anion is involved. The reaction occurs in several associative steps which do not have a reaction barrier. Implications of the results for heterogeneous reactions in the stratosphere on sulfuric acid aerosol surfaces or in the bulk are discussed.