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Real refractive indices of infrared-characterized nitric-acid/ice films: Implications for optical measurements of polar stratospheric cloudsThe infrared spectra of nitric-acid/ice films representative of polar stratospheric clouds (PSCs) were collected with simultaneous optical interference measurements to determine the real refractive indices at lambda = 632 nm. Ice and amphorous nitric-acid/ice films were prepared by condensation of water and nitric acid vapors onto a wedged Al2O3 substrate. The real refractive indices of these films were determined from the optical interference of a reflected helium-neon laser during film growth. The indices of the amphorous films varied smoothly from n = 1.30 for ice to n = 1.49 for nitric acid, similar to observations in previous work. We were unable to obtain the refractive index of crystlline films during adsorption because of optical scattering caused by surface roughness. Therefore crystlline nitric acid hydrate films were prepared by annealing amphorous nitric-acid/ice films. Further heating caused desorption of the crystalline hydrate films. During desorption, the refractive indices for ice, NAM (nitric acid monohydrate), alpha- and beta-NAT (nitric acid trihydrate) films were measured using the optical interference technique. In agreement with earlier data, the real refractive indices for ice and NAM determined in desorption were n = 1.30 +/- 0.01 and n = 1.53 +/- 0.03, respectively. The real refractive indices for alpha- and beta-NAT were found to be n = 1.51 +/- 0.01 and n greater than or equal to 1.46, respectively. Our measurements also suggest that the shape of crystalline nitric acid particles may depend on whether they nucleate from the liquid or by vapor deposition. If confirmed by future studies, this observation may provide a means of distinguishing the nucleation mechanism of crystalline PSCs.
Document ID
19950053256
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Middlebrook, Ann M.
(University of Colorado, Boulder, CO United States)
Berland, Brian S.
(University of Colorado, Boulder, CO United States)
George, Steven M.
(University of Colorado, Boulder, CO United States)
Tolbert, Margaret A.
(University of Colorado, Boulder, CO United States)
Toon, Owen B.
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
August 16, 2013
Publication Date
December 20, 1994
Publication Information
Publication: Journal of Geophysical Research
Volume: 99
Issue: D12
ISSN: 0148-0227
Subject Category
Meteorology And Climatology
Accession Number
95A84855
Funding Number(s)
CONTRACT_GRANT: NSF ATM-92-96067
CONTRACT_GRANT: NAG2-760
CONTRACT_GRANT: N00014-92-J-1365
Distribution Limits
Public
Copyright
Other

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