Ab Initio Model Study of the Mechanism of Chlorine Nitrate Hydrolysis on Ice

The hydrolysis of chlorine nitrate ClONO 2 + H 2 O → HOCl + HNO 3 on a type-II polar stratospheric cloud ice aerosol is modeled via the ClONO 2 ·(H 2 O) 3 reaction system at the HF/6-31+G** level of theory with microsolvation by three additional STO-3G waters, and with electron correlation accounted for at the MP2 level. The calculations suggest a fast reaction, consistent with experimental observations, and portray a transition state that involves a nucleophilic attack of a water molecule on chlorine concerted with proton transfer from the attacking water to the ice lattice. The results also give insight on the observed slow desorption of the produced HOCl and indicate a source of rate suppression on sulfate and nitrate containing type-I polar stratospheric cloud ice aerosols.