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Variation of the infrared spectra of nitric acid hydrates with formation conditions: Impact on PSC identification
Author(s) -
Tisdale Robert T.,
Prenni Anthony J.,
Iraci Laura T.,
Tolbert Margaret A.,
Toon O. B.
Publication year - 1999
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/1999gl900090
Subject(s) - nitric acid , infrared spectroscopy , infrared , birefringence , polar , spectral line , aerosol , extinction (optical mineralogy) , analytical chemistry (journal) , materials science , chemistry , mineralogy , inorganic chemistry , physics , optics , environmental chemistry , organic chemistry , astronomy
Despite years of effort, the composition of polar stratospheric clouds (PSCs) is still uncertain. Future studies may be able to use FTIR extinction measurements to determine PSC composition. These studies require accurate optical constants for PSC materials. It has been suggested that accurate infrared (IR) optical constants for aerosols can only be derived from aerosol spectra. We have examined the IR spectra of nitric acid trihydrate (NAT) and nitric acid dihydrate (NAD) films and aerosols formed using a variety of experimental conditions. We conclude that several spectroscopically different types of NAD and NAT may exist. Alternatively, NAT could be birefringent and its spectra depend strongly on crystallographic orientation. The important causes for the different types or orientations seem to be the formation conditions and temperature, rather than whether the material is a film or aerosol.