The rototranslational absorption spectrum of gaseous N2 is analyzed, considering quadrupolar and hexadecapolar induction mechanisms. The available experimental data are accounted for by using a line-shape analysis in which empirical profiles describe the single-line translational profiles. We thus derive the simple procedure that allows one to predict the N2 spectrum at any temperature. On the basis of the results obtained for the pure gas, we also propose a procedure to compute the far-infrared spectrum of the N2–Ar gaseous mixture. The good agreement between computed and experimental N2–Ar data indicates that it is possible to predict the far-infrared absorption induced by N2 on the isotropic polarizability of any interacting partner.
The effects of collision-induced absorption on the far infrared spectrum of Titan have been investigated. After a review of the procedure for the theoretical calculation of the N2 translation-rotational spectrum, new results for the temperature range of 70 to 120°K are reported. These are used as input data for a simple atmospheric model in order to compute the far infrared radiance, brightness temperature, and spectral limb function. This source of opacity alone is not capable of explaining the Voyager results. When the collision-induced methane is included, the results are in closer agreement in the range between 200 and 300 cm−1, suggesting that a more complete treatment of collision-induced absorption including particularly CH4-N2, N2-H2, and H2-H2 results, may provide sufficient opacity to reduce or obviate the need for opacities due to clouds or aerosols in order to explain the observed spectra.