Far Infrared CIA Spectra of N2 -CH4 Pairs for Modeling of Titan's Atmosphere

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Department of Physics


We present a simple model which allows for the computation of the rototranslational band of the collision induced absorption spectra of N2-CH4 pairs at temperatures between 70 and 300 K and at frequencies of up to ∼550 cm-1. The agreement with current experimental data has been obtained by adjusting the classical, multipole induced dipolar components by adding semiempirical quantum corrections. We have included a Q6-induction term, never considered before, which we believe is essential for the agreement we have obtained. With the set of temperature-independent parameters derived from fitting the experimental data, our model reproduces recent laboratory measurements within 124-300 K temperature and the 10-600 cm-1 frequency range, within few percent root mean square. The method provides reliable temperature dependence of the absorption coefficient as a function of frequency at temperatures as low as 70 K, which are much lower than those at which laboratory measurements are taken. The work is of significance for modeling the infrared opacity of Titan's atmosphere.

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