IONIZATION AND SOLVATION OF STRATOSPHERICALLY RELEVANT MOLECULES ON ICE FILMS

Heterogeneous reactions of stratospheric reservoir species such as HCl , N2O5 and ClONO2 on type I(nitric acid hydrates) and type II (water-i ce) polar stratospheric cloud (PSC) particles are believed to play an important role in the extremely large losses of stratospheric ozone ob served during the Antarctic spring. Laboratory studies of such process es, using thin ice films as PSC particle surface mimics, can provide m echanistic information about individual elementary steps and overall r eaction schemes. IR and mass spectrometry have been used to identify r eaction products and intermediates and it has been shown that the prim ary step in all the studied reaction schemes involves the formation of ionic surface species. Furthermore, the nature and stability of the i ons are found to be inextricably linked with the amount of 'free' wate r available to solvate them. The following questions are also addresse d: Are adsorbed ions (e.g. nitrate, chloride and oxonium) reactive on ice surfaces? If so, are the products formed the same as those suggest ed when their corresponding molecular parents are involved? The answer s, which have important implications for understanding stratospheric h eterogeneous chemistry, are discussed in terms of ionic reaction mecha nisms and novel surface intermediates.