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

Abstract : We consider the collisional excitation of H$_2$ molecule in C-type shocks propagating in dense molecular clouds. New data on collisional rate coefficients for the (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 $\zeta \gtrsim 10^{-16}$~s$^{-1}$ and at moderate shock speeds, the H/H$_2$ ratio in the shock 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 $\zeta \gtrsim 10^{-15}$~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 in interpretation of observations of H$_2$ emission in supernova remnants.
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https://hal.archives-ouvertes.fr/hal-02172344
Contributor : Aigle Clementin <>
Submitted on : Wednesday, July 3, 2019 - 5:25:17 PM
Last modification on : Tuesday, July 16, 2019 - 5:06:02 PM

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  • HAL Id : hal-02172344, version 1

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A. Nesterenok, Duncan Bossion, Yohann Scribano, Francois Lique. C-type shock modelling -- the effect of new H$_2$--H collisional rate coefficients. 2019. ⟨hal-02172344⟩

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