Far infrared absorption by collisionally interacting nitrogen and methane molecules

Quantum line shape calculations of the rototranslational enhancement spectra of nitrogen-methane gaseous mixtures are reported. The calculations are based on a recent theoretical dipole function for interacting N2 and CH4 molecules, which accounts for the long-range induction mechanisms: multipolar inductions and dispersion force-induced dipoles. Multipolar induction alone was often found to approximate the actual dipole surfaces of pairs of interacting linear molecules reasonably well. However, in the case of the N2 -CH4 pair, the absorption spectra calculated with such a dipole function still show a substantial intensity defect at the high frequencies ͑Ͼ250 cmϪ1͒ when compared to existing measurements at temperatures from 126 to 297 K, much as was previously reported.