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American Astronomical Society, Astronomical Journal, 5(146), p. 125, 2013

DOI: 10.1088/0004-6256/146/5/125

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SULFUR CHEMISTRY IN THE INTERSTELLAR MEDIUM: THE EFFECT OF VIBRATIONAL EXCITATION OF H2IN THE REACTION S++H2→SH++H

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

The Astrophysical Journal 146.5 (2013): 125, reproduced by permission of the AAS ; Specific rate constants for the S++H2 reaction are calculated using the ground quartet state potential energy surface and quasi-classical trajectories method. The calculations are performed for H 2 in different vibrational states v = 0-4 and thermal conditions for rotational and translational energies. The calculations lead to slow rate constants for the H2 vibrational levels v = 0, 1, but a significant enhancement of reactivity is observed when v > 1. The inverse reaction is also studied and rate constants for v = 0 are presented. For comparison, we also recompile previous results of state-to-state rate constants of the C ++H2 for H2 in rovibrational state v, j = (0,0), (1,0), (1,1), and (2,0). The calculated rate coefficients are fitted using an improved form of the standard three-parameter Arrhenius-like equation, which is found to be very accurate in fitting rate constants over a wide range of temperatures (10-4000 K). We investigate the impact of the calculated rate coefficients on the formation of SH+ in the photon-dominated region Orion Bar and find an abundance enhancement of nearly three orders of magnitude when the reaction of S+ with vibrationally excited H2 is taken into account. The title reaction is thus one of the principal mechanisms in forming SH+ in interstellar clouds