Computer Science
Scientific paper
Jun 1991
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1991phdt........20n&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF MARYLAND COLLEGE PARK, 1991.Source: Dissertation Abstracts International, Volume: 52-06, Section:
Computer Science
Scientific paper
Methane (CH_4) is among the most abundant simple organic compounds in the outer planets. It is expected to form cloud particles on Uranus, it forms ice on the surface of Pluto and Triton (the moon of Neptune) and together with ethane (C_2 H_6), it should form global oceans on Titan. C_2H_6 , acetylene (C_2H _2) and diacetylene (C_4H _2) are expected to form a stratospheric haze on Uranus. The haze reflects and scatters ultraviolet radiation, absorbs visible radiation and emits infrared radiation. In the atmosphere of Titan, ultraviolet photolysis of CH_4 and electron bombardment of N_2 produce more complex hydrocarbons and nitriles. Some of the expected but not yet detected species include acetonitrile (CH_3CN), propionitrile (C_2H_5 CN) and acrylonitrile (CH_2CHCN). To carry out radiative transfer calculations, to study the reflection of radiation from the surface of the planets and to model the radiative heating in the stratosphere due to infrared emission, the optical constants of the condensed phases of these materials are desired for a wide temperature range. In this dissertation, the optical constants, alpha (absorption coefficient), n and k (n^* = n + ik, the real and imaginary parts of the complex refractive index) for these solids are presented for several temperatures for the 5000 -450 cm^{-1} (2-22.2 μm) region. For this work, a special cell for carrying out temperature dependent spectral studies was designed and constructed. The data for hydrocarbons are also presented for the 10,000-5000 cm^ {-1} (1-2 μm) region. The optical constants for the nitriles, CH_3 CN, C_2H_5 CN and CH_2CHCN are presented from 5000-450 cm^{-1}. Thin films of the compounds were prepared by slowly depositing the gas onto the substrate of a conventional cryocooler or onto the window of a stainless steel cell. The amorphous material was annealed and the infrared spectra were recorded at several temperatures. The absorption coefficients, and complex refractive indices in the mid infrared (5000-450 cm^{-1}) were calculated by an iterative Kramers Kronig analysis. The extinction coefficients for the absorption of the crystalline compounds in the near infrared (10,000-5000 cm ^{-1}) were also calculated.
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