Spectroscopic studies of model polar stratospheric cloud films

摘要

Abstract: Fourier transform infrared (FTIR) spectroscopy has been used to study nitric-acid/ice films representative of type I polar stratospheric clouds (PSCs). These studies reveal that in addition to amorphous nitric acid/ice mixtures, there are three stable stoichiometric hydrates of nitric acid: nitric-acid monohydrate (NAM), dihydrate (NAD) and trihydrate (NAT). We also observe two distinct crystalline forms of the trihydrate, which we denote $alpha@- and $beta@-NAT. These two forms appear to differ in their concentration of crystalline defects, but not in their chemical composition. In addition to probing the composition of type I PSCs, we have also used FTIR spectroscopy to study the interaction of HCl with model PSC films. In this work we find that for HCl pressures in the range 10$+$MIN@5$/ - 10$+$MIN@7$/ Torr, HCl is taken up by ice at 155 K to form a thin layer of HCl $DOT 6H$-2$/O. At 193 K, the uptake of HCl by ice was consistent with $LSEQ monolayer coverage. Uptake of HCl by $alpha@- and $beta@-NAT at 175 K was also consistent with $LSEQ monolayer coverage. !18