Molecular Friction in Dilute Gases. II. Thermal Relaxation of Translational and Rotational Degrees of Freedom

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Abstract
Expressions for the rates of equilibration of the translational energies in multicomponent gas mixtures of structureless molecules are derived in terms of characteristic relaxation times. The approach to equilibrium is found to be completely dominated by an exponential decay factor for molecules interacting with inverse power potentials; the decay should be essentially exponential for more realistic potential functions. The calculations of rotational relaxation times are presented for several rigid molecular models: rough and partially rough spheres, spherocylinders, and loaded spheres. The relaxation times obtained are in good agreement with those observed experimentally and with those predicted by previous theories. It is found that, in general, on the order of 10 collisions are required to reduce an initial temperature difference by a factor of 1/e for translational‐rotational equilibration.

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