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Description
Spectra and optical constants of nitrile ices known or suspected to be in Titan's atmosphere are presented from 2.0 to 333.3um (~5000-30/cm). These results are relevant to the ongoing modeling of Cassini CIRS observations of Titan's winter pole. Ices studied are: HCN, hydrogen cyanide; C2N2, cyanogen; CH3CN, acetonitrile; C2H5CN, propionitrile; and HC3N, cyanoacetylene. For each of these molecules, we also report new cryogenic measurements of the real refractive index, n, determined in both the amorphous and crystalline phases at 670nm. These new values have been incorporated into our optical constant calculations. Spectra were measured and optical constants were calculated for each nitrile at a variety of temperatures, including, but not limited to, 20, 35, 50, 75, 95, and 110K, in both the amorphous phase and the crystalline phase. This laboratory effort used a dedicated FTIR spectrometer to record transmission spectra of thin-film ice samples. Laser interference was used to measure film thickness during condensation onto a transparent cold window attached to the tail section of a closed-cycle helium cryostat. Optical constants, real (n) and imaginary (k) refractive indices, were determined using Kramers-Kronig analysis. Our calculation reproduces the complete spectrum, including all interference effects.
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