Semiclassical theory of the effects of collisions between rotors on molecular spectral line shapes. I

The semiclassical (WKB) limit of the quantum mechanical expression for the collisional line broadening cross section of the microwave spectrum of gaseous molecules is derived. For the present purpose of considering binary collisions between such species as OCS and CO2, action-angle-like variables for the classical mechanics of two interacting rotors are developed. Applications can be made to the evaluation of T2 (microwave line broadening) and T1 (microwave transient experiments) cross sections and to calculations of rotational and vibrational energy transfer for linear molecule–linear molecule systems.