Recently, chlorocompound/ice and nitrocompound/ice reactions have been proposed as key heterogeneous steps in the process leading to destruction of Antarctic stratospheric ozone. In order to understand the role of the ice during the process, there is a need for new laboratory techniques that (1) yield accurate molecular-level data on ice surfaces and associated adspecies and (2) allow in situ on-surface monitoring of chemistry on ice crystals. Whereas most surface science techniques are not suitable for high vapor pressure insulating substrates, the new surface sensitive laser technique, second harmonic generation (SHG), has great potential for probing chemistry of this kind. SHG signals produced by a tunable, sub-picosecond laser directly yield highly accurate data such as sticking coefficients electronic spectra and orientations of molecules comprising a single monolayer on an insulating surface. SHG will be utilized for the first time on ice surfaces, to isolate and examine key steps in the stratospheric ozone depletion chemistry: adsorption, reaction and desorption processes of compounds such as CIONO2 and N2O5. In order to simulate stratospheric ice, a single crystal ice sample is housed in a temperature and pressure controlled chamber. An important aspect of the study is a novel method for studying the effects of ice composition (HCl and HNO3 content) on the reactions. The objectives are to (1) accurately quantify reaction parameters at various temperatures from data taken directly at the ice surface and (2) understand the mechanisms of the surface reactions.
