Coupled radiative and vibrational nonequilibrium in a diatomic gas, with application to gas dynamics

Abstract

Macroscopic equations are formulated for the nonequilibrium interaction of radiative and vibrational rate processes in an infrared-active diatomic gas. Radiative transitions are taken into account initially in a microscopic formulation for a general two-level system, with line broadening included. The macroscopic equation of radiative transfer for the multi-level system is then obtained by summation of the microscopic equation, specialized to a harmonic-oscillator rigid-rotor molecule, over all rotational and vibrational transitions. The resulting transfer equation is necessarily coupled to the vibrational rate equation, which is formulated heuristically on the basis of energy-exchange mechanisms and the established model for collisional relaxation. The entire development is influenced by its intended application in radiative gas dynamics. Such application is illustrated in its simplest form by the development of the corresponding acoustic theory.