Rotationally inelastic collisions between H2 molecules in interstellar magnetohydrodynamical shocks

We present the results of quantum mechanical calculations of the rates of rotational transitions in ortho- and para-H2 induced in collisions with other H2 molecules. Transitions ΔJ = 2 between rotational levels J ⩽ 7 are considered. Some possible approximations in the collision calculation are discussed and found to give results of an accuracy which is acceptable for the intended astrophysical applications, to the theoretical study of interstellar MHD shocks. Comparison is made with earlier calculations of H2–H2 scattering by Monchick & Schaefer and of He–H2 scattering by Schaefer. The rate coefficients for transitions induced by ortho-H2 (J = 1) are found to be remarkably similar to the rate coefficients for the same transitions induced by He, particularly at the lower temperatures considered.