Molecular Collisions. IV. Nearly Spherical Rigid Body Approximation

Rotational transitions in the collisions of diatomic molecules are treated by means of a rigid body approximation. The deviation from sphericity is assumed to be sufficiently small that it may be treated as a perturbation. The differential cross section is calculated for the H2-HD collision in which the hydrogen remains in its ground state while the hydrogen deuteride goes from its ground state to the first excited rotational state.