12 February 1993 Spectroscopic studies of model polar stratospheric cloud films
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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 10-5 - 10-7 Torr, HCl is taken up by ice at 155 K to form a thin layer of HCl (DOT) 6H2O. At 193 K, the uptake of HCl by ice was consistent with <EQ monolayer coverage. Uptake of HCl by (alpha) - and (beta) -NAT at 175 K was also consistent with <EQ monolayer coverage.
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Margaret A. Tolbert, Margaret A. Tolbert, Birgit G. Koehler, Birgit G. Koehler, Ann M. Middlebrook, Ann M. Middlebrook, "Spectroscopic studies of model polar stratospheric cloud films", Proc. SPIE 1715, Optical Methods in Atmospheric Chemistry, (12 February 1993); doi: 10.1117/12.140234; https://doi.org/10.1117/12.140234
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