21 July 1994 Characterization of model polar stratospheric cloud films using laser-induced thermal desorption and optical interference techniques
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Proceedings Volume 2125, Laser Techniques for Surface Science; (1994) https://doi.org/10.1117/12.180862
Event: OE/LASE '94, 1994, Los Angeles, CA, United States
Abstract
Optical interference techniques were used to measure the real index of refraction of nitric acid/ice films representative of type I and type II polar stratospheric clouds (PSCs). Possible candidates for type I PSCs include amorphous HNO3/H2O mixtures, as well as crystalline nitric acid trihydrate, dihydrate (NAD), and monohydrate (NAM). Amorphous and crystalline model PSC films were grown in vacuum by vapor deposition on single-crystal Al2O3 substrates at low temperatures. The real indices of refraction at (lambda) equals632 nm were measured for these films using the time-dependent optical interference during film deposition. The stoichiometries of the HNO3/H2O films were determined using laser induced thermal desorption techniques. For the amorphous films at 130 K, the refractive indices increased with increasing nitric acid content. The values ranged from nequals1.31+/- 0.01 for pure ice to nequals1.47+/- 0.01 for nearly pure nitric acid. A Lorentz-Lorenz analysis was in good agreement with the measured refractive indices of the amorphous HNO3/H2O films as a function of HNO3 mole fraction. Growth of HNO3/H2O films at 175 K resulted in the formation of either crystalline NAM or NAD. The crystalline indices were substantially higher than their amorphous analogs. The crystalline refractive indices at 175 K were in nequals1.52+/- 0.01 for NAD and nequals1.54+/- 0.01 for NAM.
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Brian S. Berland, D. Haynes, Krishna L. Foster, Margaret A. Tolbert, Steven M. George, O. B. Toon, "Characterization of model polar stratospheric cloud films using laser-induced thermal desorption and optical interference techniques", Proc. SPIE 2125, Laser Techniques for Surface Science, (21 July 1994); doi: 10.1117/12.180862; https://doi.org/10.1117/12.180862
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