Quantum mechanical computations of collision-induced absorption in the second overtone band of hydrogen

The second overtone band of hydrogen is important for studies of both planetary and stellar atmospheres. Until recently, only one experimental measurement existed, taken at 85 K (McKellar, Welsh. Proc Roy Soc London Ser A 1971;322:421). In this paper we present the first quantum mechanical computations of the collision-induced rotovibrational absorption spectra of H-2 pairs in the second (3-0) overtone band of hydrogen. We compare our computations with the data by McKellar and Welsh. The second overtone band is very weak and thus it is extremely difficult to measure it in the laboratory, as well as to compute it based on the first principles. As it appears, the collision-induced dipoles of H-2 pairs, which give rise to this CIA band spectra are so weak, that the numerical results, at some particular mutual orientations, are almost at the level of numerical uncertainty. Our computations are based on an extension of a database of H-2-H-2 collision-induced dipoles which already exists (Meyer et al. Phys Rev A 1989;39:2434-48) but which is inadequate for computing CIA bands of hydrogen at overtones higher than the first overtone, (C) 2000 Elsevier Science Ltd. All rights reserved.