On the Relaxation of Vibrational Nonequilibrium Distributions. III. The Effect of Radiative Transitions on the Relaxation Behavior

In previous papers of this series (Parts I and II) a theoretical study has been made of the collisional relaxation of a system of harmonic oscillators (with hv/kT≪1) from initial vibrational nonequilibrium distributions and of the influence of the collisional transition probabilities on the relaxation behavior. This paper is concerned with the extension of this study to include the effects of concurrent radiative transitions on the relaxation behavior. It was found that concurrent radiative transitions do not change the relaxation behavior of the system of harmonic oscillators from that found previously for purely collisional transitions. The only change is in the time-scale of the relaxation in that the expressions obtained in Part I must be multiplied by a factor of the form exp[—t/τ] where τ is the lifetime of the oscillators in their excited vibrational and electronic energy levels.