On the Physical Meaning of the Parameters of Intermolecular Interaction Potentials in the Asymptotic Line Wing Theory

Formulas for the absorption coefficient in the asymptotic line wing theory (ALWT) in spectral regions far from the centers of strong lines are derived. The quantum and classical problems are separated using the semiclassical representation method. The classical potential, which describes the motion of the centers of mass of molecules, is also part of the definition of the second virial coefficient. It is shown that the temperature dependence of the second virial coefficient defines the temperature dependence of the absorption coefficient in terms of the classical potential. The parameters of the quantum potential of the intermolecular interaction (IMI), adjusted to agree with the experimental absorption data, approximate the difference between the quantum energies of interaction of colliding molecules in different vibrational states. The quantum-mechanical calculations of differences between these energies were analyzed for the CO–Ar, CO₂–Ar, and CO₂–He systems. A comparison of the results with approximations obtained in calculations of absorption coefficients shows that the shapes of the curves depending on the distance between the centers of mass are reproduced, differing only by constants. Thus, the parameters of potentials used in ALWT agree with the thermodynamic data (classical potential) and with quantum-mechanical calculations of potential surfaces (quantum potential), which confirms their physical meaning.