C-type shock modelling -- the effect of new H$_2$-H collisional rate coefficients

A. V. Nesterenok; D. Bossion; Y. Scribano; F. Lique

doi:10.1093/mnras/stz2441

paper

C-type shock modelling -- the effect of new H $_{2}$ -H collisional rate coefficients

arXiv:1909.07738 · doi:10.1093/mnras/stz2441

Abstract

We consider collisional excitation of H $_{2}$ molecules in C-type shocks propagating in dense molecular clouds. New data on collisional rate coefficients for (de-)excitation of H $_{2}$ molecule in collisions with H atoms and new H $_{2}$ dissociation rates are used. The new H $_{2}$ -H collisional data are state of the art and are based on the most accurate H $_{3}$ potential energy surface. We re-examine the excitation of rotational levels of H $_{2}$ molecule, the para-to-ortho-H $_{2}$ conversion, and H $_{2}$ dissociation by H $_{2}$ -H collisions. At cosmic ray ionization rates $ζ \geq 1 0^{- 16}$ s $^{- 1}$ and at moderate shock speeds, the H/H $_{2}$ ratio at the shock front is mainly determined by the cosmic ray ionization rate. The H $_{2}$ -H collisions play the main role in the para-to-ortho-H $_{2}$ conversion and, at $ζ \geq 1 0^{- 15}$ s $^{- 1}$ , in the excitation of vibrationally excited states of H $_{2}$ molecule in the shock. The H $_{2}$ ortho-to-para ratio (OPR) of the shocked gas and column densities of rotational levels of vibrationally excited states of H $_{2}$ are found to depend strongly on the cosmic ray ionization rate. We discuss the applicability of the presented results to interpretation of observations of H $_{2}$ emission in supernova remnants.

10 pages, 4 figures, accepted for publication in MNRAS

C-type shock modelling -- the effect of new H2​-H collisional rate coefficients

Abstract

C-type shock modelling -- the effect of new H $_{2}$ -H collisional rate coefficients