Rotational and Vibrational Relaxation in Diatomic Gases

Calculations of rotational and vibrational relaxation times for gases composed of homonuclear diatomic molecules have been carried out. The model used for the molecular interaction potential consists of an attractive component, which acts between geometrical centers of the molecules, and a repulsive component which is assumed to originate from two centers of force in each of the molecules. For large intermolecular separations, the attractive forces prevail while at close distances the repulsive forces control. Using this model, the number of collisions to establish rotational equilibrium ZR and also the number for vibraton ZV are calculated. Both ZR and ZV contain some of the same molecular parameters and are therefore dependent on each other. From the analysis it turns out that ZR is a gradually increasing function of increasing temperature and ZV is a rapidly decreasing function of increasing temperature. Comparison with experiment for the gases chlorine, nitrogen, and oxygen indicates that the calculations are for the most part reliable.