Characterization of model polar stratospheric cloud films using laser-induced thermal desorption and optical interference techniques

Brian S. Berland; D. Haynes; Krishna L. Foster; Margaret A. Tolbert; Steven M. George; O. B. Toon

doi:10.1117/12.180862

21 July 1994 Characterization of model polar stratospheric cloud films using laser-induced thermal desorption and optical interference techniques

Brian S. Berland, D. Haynes, Krishna L. Foster, Margaret A. Tolbert, Steven M. George, O. B. Toon

Author Affiliations +

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, and 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); https://doi.org/10.1117/12.180862

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