COLLISION-INDUCED ABSORPTION OF H-2-H-2 AND H-2-HE IN THE ROTATIONAL AND FUNDAMENTAL BANDS FOR PLANETARY APPLICATIONS

In recent years there has been significant progress in the ab initio c omputation and modeling of the collision-induced absorption in H-2-H-2 and H-2-He pairs in the rotovibrational and purely rototranslational bands covering 0-6000 cm(-1) at temperatures from 40 to 300 K. Extensi ve 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 o n this subject and presents a number of new results. Moreover, this re port is designed to facilitate the utilization of this knowledge for t he study of planetary atmospheres, and for future research of the H-2- H-2 and H-2-He infrared spectra. The theoretical absorption coefficien ts arising from free-free transitions in collisional pairs are availab le in the form of FORTRAN programs which permit rapid and reliable eva luation of spectral intensities even for frequencies and temperatures at which laboratory measurements do not exist. The various approximati ons affecting the accuracy of the theory applied here are discussed in some detail. The theoretical spectra closely duplicate the existing l aboratory measurements of collision-induced absorption, whose accuracy is discussed; only for the case of the fundamental band of H-2-He are there small discrepancies from recent measurements which exceed somew hat the combined uncertainties of theory and measurement. The simple a nalytical functions on which these computer programs are based have al so been compared with the quantum mechanical computations of the spect ra and very close agreement has been observed. Notes regarding the use of the computer programs and sample outputs are given to serve as a t est for their applications. (C) 1996 Academic Press, Inc.