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 collision-induced rotational translational spectrum of gaseous N2 has been measured in the temperature range 228–343 K at six different temperatures. The measurements were made with a Fourier transform spectrometer in the 25 to 360 cm−1 region and at 15.1 and 84.2 cm−1 with far infrared (FIR) laser. Previously obtained microwave data at 2.3 and 4.7 cm−1 have been used in defining the complete spectrum. Using a recently developed theory for quadrupolar-induced absorption, we find that the calculated quadrupole moment is independent of temperature and has a magnitude in close agreement with the recommended values of several other workers; i.e., Q = 1.46 B. The calculated value depends on the particular form of the intermolecular potential and this dependence is examined in some detail. A contribution to the absorption originating primarily from hexadecapolar and overlap induction has been observed in agreement with theoretical estimates and leads to an estimated value for the hexadecapolar moment φ=3.4*10-42 esu cm4.
Pure N2 absorption spectrum at 149°K: ----. best fit.
Pure N2 absorption spectrum at 149°K: - - -, hexadecapolar component.
Pure N2 absorption spectrum at 149°K: ... , experimental data from Ref.
Stone, N. W. B., Read, L. A. A., Anderson, A., Dagg, I. R., & Smith, W., Temperature dependent collision-induced absorption in nitrogen, Canadian journal of physics, 62(4), 338-347. (1984).
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.
The rototranslational absorption spectrum of N2-H2 gaseous mixtures has been measured at five different temperatures from 298 to 90 K in the frequency range 80–850 cm-1. The absorption spectra due to N2-H2 interactions have been analyzed considering only the quadrupolar induction mechanism. With this assumption, the experimental data are fairly well accounted for, thereby providing a procedure for predicting the N2-H2 spectrum over a wide temperature range.