Theoretical calculation of the translation-rotation collision-induced absorption in N₂-N₂, O₂-O₂, and N₂-O₂ pairs

Abstract

The translation-rotation collision-induced spectra of N₂-N₂, O₂-O₂, and N₂-O₂ mixtures are calculated theoretically. For N₂-N₂, using the matrix elements for the quadrupole and hexadecapole moments and the isotropic and anisotropic polarizabilities obtained previously from a global analysis of the fundamental band spectra, we obtain numerical values for the zero'th moment that are smaller than the measured values by 9-14%, depending on the temperature. By increasing the value for the matrix element of the isotropic polarizability slightly, good agreement with experiment is obtained. For O₂-O₂, the theoretical spectrum is significantly smaller than the experimental result. By increasing the matrix element of the hexadecapole moment by a factor of 1.7, we can obtain good agreement. This larger value for the hexadecapole moment will not appreciably affect the agreement found previously in the fundamental region because the hexadecapole contribution to the intensity is very small, unlike the translation-rotation band where it is larger than the contribution dur to the quadrupole moment. Using these parameters, we then calculate the collision-induced absorption for air, and compare our results with previous work; we express the results for the ratio of the absorption coefficient of air to that of N₂-N₂ as a function of wavenumber and temperature, R(w,T), which can easily be implemented in atmospheric models.

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