State-to-state rate constants for the title reaction are calculated using the electronic ground state potential energy surface and an accurate quantum wave-packet method. The calculations are performed for H2 in different rovibrational states, v = 0, 1 and J = 0 and 1. The simulated reaction cross section for v = 0 shows a rather good agreement with the experimental results of Gerlich et al., both with a threshold of 0.36 eV and within the experimental error of 20%. The total reaction rate coefficients simulated for v = 1 are two times smaller than those estimated by Hierl et al. from cross sections measured at different temperatures and neglecting the contribution from v > 1 with an uncertainty factor of two. Thus, part of the disagreement is attributed to the contributions of v > 1. The computed state-to-state rate coefficients are used in our radiative transfer model code applied to the conditions of the Orion Bar photodissociation region, and leads to an increase of the line fluxes of high-J lines of CH+. This result partially explains the discrepancies previously found with measurements and demonstrates that CH+ excitation is mostly driven by chemical pumping. © 2013. The American Astronomical Society. All rights reserved..

Thiswork has been supported by the program CONSOLIDER-INGENIO 2010 of the Ministerio de Ciencia e Innovacion under grant CSD2009-00038, entitled “Molecular Astrophysics: the Herschel and Alma era,” and by grant No. FIS2010-18132, and by Comunidad Autonoma de Madrid (CAM) under grant No. S-2009/MAT/1467. The calculations have been performed in the parallel facilities at the CESGAcomputing center through ICTS grants, which are acknowledged.

8 pags., 6 figs., 1 tab.

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