AB-INITIO MODEL STUDY OF THE MECHANISM OF CHLORINE NITRATE HYDROLYSISON ICE

The hydrolysis of chlorine nitrate ClONO2 + H2O --> HOCl + HNO3 on a t ype-II polar stratospheric cloud ice aerosol is modeled via the ClONO2 .(H2O)(3) reaction system at the HF/6-31+G* level of theory with mic rosolvation by three additional STO-3G waters, and with electron corre lation accounted for at the MP2 level. The calculations suggest a fast reaction, consistent with experimental observations, and portray a tr ansition state that involves a nucleophilic attack of a water molecule on chlorine concerted with proton transfer from the attacking water t o the ice lattice. The results also give insight on the observed slow desorption of the produced HOCl and indicate a source of rate suppress ion on sulfate and nitrate containing type-I polar stratospheric cloud ice aerosols.