Collision-induced absorption of H2-H2 and H2-He in the rotational and fundamental bands for planetary applications

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Department of Physics


In recent years there has been significant progress in the ab initio computation and modeling of the collision-induced absorption in H2-H2 and H2-He pairs in the rotovibrational and purely rototranslational bands covering 0-6000 cm-1 at temperatures from 40 to 300 K. Extensive experimental and theoretical results have been obtained in a number of laboratories regarding this absorption as a function of frequency and temperature. This report summarizes the most advanced literature on this subject and presents a number of new results. Moreover, this report is designed to facilitate the utilization of this knowledge for the study of planetary atmospheres, and for future research of the H2-H2 and H2-He infrared spectra. The theoretical absorption coefficients arising from free-free transitions in collisional pairs are available in the form of FORTRAN programs which permit rapid and reliable evaluation of spectral intensities even for frequencies and temperatures at which laboratory measurements do not exist. The various approximations affecting the accuracy of the theory applied here are discussed in some detail. The theoretical spectra closely duplicate the existing laboratory measurements of collision-induced absorption, whose accuracy is discussed; only for the case of the fundamental band of H2-He are there small discrepancies from recent measurements which exceed somewhat the combined uncertainties of theory and measurement. The simple analytical functions on which these computer programs are based have also been compared with the quantum mechanical computations of the spectra and very close agreement has been observed. Notes regarding the use of the computer programs and sample outputs are given to serve as a test for their applications.

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