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 plane tary and stellar atmospheres. Until recently, only one experimental measure ment existed, taken at 85 K (McKellar, Welsh. Proc Roy Soc London Ser A 197 1;322:421). In this paper we present the first quantum mechanical computati ons of the collision-induced rotovibrational absorption spectra of H-2 pair s in the second (3-0) overtone band of hydrogen. We compare our computation s with the data by McKellar and Welsh. The second overtone band is very wea k and thus it is extremely difficult to measure it in the laboratory, as we ll as to compute it based on the first principles. As it appears, the colli sion-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 orienta tions, are almost at the level of numerical uncertainty. Our computations a re 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 i s inadequate for computing CIA bands of hydrogen at overtones higher than t he first overtone, (C) 2000 Elsevier Science Ltd. All rights reserved.