On the interpretation of measured rotational and vibrational relaxation times. I. Sound dispersion experiments

Abstract

The simultaneous relaxation to equilibrium of both rotational and vibrational populations is considered for a diatomic molecule immersed in a heat bath of inert-gas atoms. The relaxation is analyzed in terms of normal modes of relaxation, and it is shown that each mode, having its own distinct relaxation time, in general has both rotational and vibrational components. The qualitative form of these modes is very persistent, and survives considerable variations in the assumed temperature and the assumed set of transition probabilities. Using these modes of relaxation, an approximate treatment is given of the contribution made by the diatomic gas to the sound dispersion of the mixture, and conditions under which modes of relaxation may or may not be resolved from each other, or may be characterized as either 'rotational' or 'vibrational' are examined.