Transport Properties of a Gas of Diatomic Molecules

Explicit expressions, valid in the classical limit, are derived for the rotational relaxation time and viscosity of a low-density gas of rotating, nonvibrating, diatomic molecules. These expressions are based on the quantum mechanical expressions in terms of the degeneracy-averaged cross sections for a gas in which the average angular momentum of the molecules is zero. The use of an expression for the classical limit of the degeneracy-averaged cross section leads to the evaluation of several of the summations and integrations.