The classical Boltzmann equation of a gas of diatomic molecules

A classical Boltzmann equation and collision integral of a gas of nonvibrating diatomic molecules is developed. It is shown that the generalization of the usual equation for structureless particles involves additional integrations over the angular momentum vector of the second molecule and two angles associated with the phases of the rotational motion of the two molecules. These latter angles are constants of the free motion of the molecules defined in a manner analogous to that of the usual impact parameter, i.e., they are determined by the free molecule trajectory as extrapolated to the point of closest approach.