Astronomy and Astrophysics – Astrophysics
Scientific paper
Jan 1990
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1990phdt........80m&link_type=abstract
Thesis (PH.D.)--UNIVERSITY OF MARYLAND COLLEGE PARK, 1990.Source: Dissertation Abstracts International, Volume: 51-05, Section:
Astronomy and Astrophysics
Astrophysics
Scientific paper
Complex photochemistry in the stratosphere of Titan's north pole produces a large number of hydrocarbons and nitriles which condense as aerosal clouds at or near the tropopause. The Voyager I IRIS spectrum of Titan's north limb contains a few peaks which may be due to the condensed phases of four nitriles: HCN (hydrogen cyanide) at 828 cm^{-1}, HC _3N (cyanoacetylene) at 505 cm^ {-1}, C_4N _2 (dicyanoacetylene) at 478 cm^ {-1} and H_3C _4N (cyanopropyne) at 504 cm^ {-1}. Infrared spectra of thin crystalline films of the materials were recorded and the absorption intensities, alpha, and complex refractive indices, n and k (where n^{*} = n + ik), were determined using a Kramers-Kronig analysis. These help astrophysical modelers calculate the abundances of these compounds in Titan's atmosphere. In order to make these radiative transfer models internally consistent, it is also necessary to know the vapor pressures of the nitriles at low temperatures. Two methods were used to determine them. The first was the direct measurement of the vapor pressure of the sample with a capacitance manometer while the sample was immersed in a low temperature slush bath. This method measures pressures from 10 ^{-3} to 100 Torr. For pressures below this, a new method was developed; the thin film infrared method (TFIR) uses infrared spectroscopy to measure the disappearance rate of a thin film of the sample at a particular temperature. This rate is then related to the vapor pressure and was used to measure pressures from 10^ {-8} to 10^{-6} Torr. These values differed by as much as two orders of magnitude from the values obtained by extrapolating existing high temperature data using the Clausius-Clapeyron equation.
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