Abstract
We consider collisional excitation of H2 molecules in C-type shocks propagating in dense molecular clouds. New data on collisional rate coefficients for (de-)excitation of H2 molecule in collisions with H atoms and new H2 dissociation rates are used. The new H2–H collisional data are state of the art and are based on the most accurate H3 potential energy surface. We re-examine the excitation of rotational levels of H2 molecule, the para-to-ortho-H2 conversion,and H2 dissociation by H2–H collisions. At cosmic ray ionization rates ζ>10−16s−1and at moderate shock speeds, the H/H2 ratio at the shock front is mainly determined by the cosmic rayionization rate. The H2–H collisions play the main role in the para-to-ortho-H2 conversion and, at ζ>10−15s−1, in the excitation of vibrationally excited states of H2 molecule in the shock. The H2 ortho-to-para ratio (OPR) of the shocked gas and column densities of rotational levels of vibrationally excited states of H2 are found to depend strongly on the cosmic ray ionization rate. We discuss the applicability of the presented results to interpretation of observations of H2 emission in supernova remnants.