2013AJ....146..125Z

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 H₂ 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 H₂in 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.