Rate Enhancement of the Reaction of HCl with ClONO2 by Ions: Implications for the Mechanisms of Stratospherically Important Heterogeneous Reactions

We report the first observation of the ion-assisted neutral reaction of HCl with ClONO2. These two species react efficiently in the gas phase to form nitric acid and chlorine when one or the other is clustered to an NO3- core ion. Utilizing a selected ion flow tube we find that reaction 1 proceeds with a rate coefficient of 1.8 x 10exp -9 cu cms at 233 K and that reaction 2 proceeds with a rate coefficient of 1.5 x 10exp -9 cu cms at 283 K, values near the collision rate coefficient. Minor channels involving ligand switching were also observed. In contrast, the rate coefficient for the neutral species HCl and ClONO2 is small, less than 1 x 10exp -20 cu cms. Few reactions of this type, where the core ion enhances the rate of the reaction without apparently being chemically transformed, have been reported.