On the problem of detailed balance and model lineshapes in collision-induced rotovibrational bands: H(sub)2-H(sub)2 and H(sub)2-He

When account is taken of the vibrational dependence of the potential function, the usual condition of detailed balance taken with respect to the vibrational-rotational frequencies do not apply, and model spectral functions satisfying this condition are inaccurate. A model correlation function is derived that deals with the case of vibration-dependent potentials. The parameters of the model are computed from relations involving the spectral moments. This model is shown to give spectral shapes, for a number of examples involving the fundamental and first overtone bands of H2-He and H2-H2 at room temperature and 1000 K, in excellent agreement with spectra calculated quantum mechanically from first principles. The model is useful for predicting the collision-induced vibrational spectra for these and other systems for which the vibration-dependent induced dipole and potential are known. (author)