Theoretical collision-induced rototranslational absorption spectra for modeling Titan's atmosphere - H2-N2 pairs

Abstract

The collision-induced rototranslational absorption coefficient of the H2-N2 molecular complex at frequencies from 0 to beyond 1000/cm, and at temperatures from 50 to 300 K (for which no laboratory measurements exist), is computed from theory. Quadrupolar and hexadecapolar induction of both species, H2 and N2, are accounted for, and a rigorous quantum line shape formalism combined with numerical procedures is used. The present uncertainties of computed intensities arise mainly from the uncertainties of the H2-N2 interaction potential. For the first time, a theoretical description of the spectral features of H2-N2 dimers in the isotropic potential approximation is given. The work is of interest for a detailed analysis of the Voyager IRIS spectra of Titan's atmosphere, especially in the regions of the rotational S0 and S0(1) lines of hydrogen, from about 200 to 700/cm. Exact line shape calculations are complex and expensive. Therefore, simple, six-parameter model line shape functions are defined which allow the reproduction of results of quantum calculations in seconds, on computers of small capacity, with a numerical accuracy of better than 2 percent.