Collision-induced infrared spectra of H2-He pairs involving 0-1 vibrational transitions and temperatures from 18 to 7000 K

Abstract

For the fundamental (2.3 fim) band of hydrogen (which involves vibrational quantum numbers p = 0-n/ = 1) the spectral profile, a(co; T), and the three lowest spectral moments, M nfVV (T) with n = 0, 1, and 2, of the collision-induced absorption spectra of H 2-He pairs are computed from first principles using a rigorous quantum formalism. The range of temperatures T considered is from 18 to 7000 K. With the help of a novel procedure which accounts for the first time for the proper asymmetry of the observed line profiles arising from the dependence of the interaction potential on the vibrational coordinate, a simple but accurate analytical model of the CIA spectra is obtained. The spectra, which can be computed in seconds even on small computers, are in close agreement with the presently known laboratory measurements and extrapolate these dependably to higher as well as to lower temperatures, and to higher frequencies. The work is of interest for the modeling of the atmospheres of the outer planets and certain cool stars that contain neutral molecular hydrogen and helium (late stars, white dwarfs, Population III stars) in the near-infrared region of the spectrum .