The excitation of molecular hydrogen by atomic hydrogen in astrophysical media

We report calculations of rate coefficients for the rovibrational excitation of H2 and HD by H. The calculations relate explicitly to non-reactive scattering, excluding the proton-exchange channels. For vibrationally inelastic transitions, the new rate coefficients at T≈ 1000 K are larger than the results of earlier calculations in which the vibrational motion was treated approximately, by means of a simple harmonic oscillator model. As a result, much better agreement is obtained with the empirical estimates by Allers et al. of the rate coefficients for vibrational relaxation of the levels (v, j) = (1, 3) and (2, 3) of H2. However, the effects of the new data on the results of illustrative astrophysical models – of a C-type shock wave and of the gravitational collapse of a condensation of the primordial gas – are less pronounced than the changes to the rate coefficients for vibrationally inelastic transitions might suggest; we explain why this is the case.