Three-body induced dipole moments and infrared absorption: The H2 fundamental band.

Abstract

In a previous paper [Phys. Rev. A 40, 6260 (1989)] the ternary absorption coefficient of hydrogen in the fundamental band was calculated with the assumption of pairwise dipole components. The comparison with measurements of the absorption showed striking disagreement, particularly at the higher temperatures, presumably due to the neglect of the irreducible ternary dipole components. We extend here the calculations by including the most important irreducible ternary dipole components. The overlap-induced part of the ternary dipole components is obtained from the one-effective electron model which is written in a form suitable to account for vibrational transitions. Two different models are compared here: one suggested by Guillot [ital et] [ital al]., J. Chem. Phys. 90, 650 (1989), and a new one. The comparison of the calculated total absorption (a sum formula) with the existing measurements shows that in hydrogen the exchange quadrupole-induced ternary dipole components are capable of producing the strong observed temperature dependence. Furthermore, it is the only mechanism presently known which may permit the reproduction of the measured data from theory; some of the approximations developed here give reasonable quantitative agreement with the measurement.