Transport Properties of a Gas of Diatomic Molecules. IV. Classical Limit

The differential cross sections for rotational excitation in collisions of diatomic molecules may be expressed in terms of the generalized phase shift, H(l̄SaSb). As with the usual phase shift, η(l̄), a semiclassical expansion of ℏ H(l̄SaSb) begins with a term of zero order in ℏ. Unlike the expansion of ℏ η(l̄), however, the next term in the expansion of ℏ H(l̄SaSb) is a purely imaginary term of order ℏ. The effect of this term in the expansion on the classical limit of certain sums and integrals of the cross sections related to the transport coefficients is considered.