2017MNRAS.472..738L

Among interstellar chlorine bearing molecules, HCl is certainly the most useful probe for studying chlorine chemistry since it is formed at the end of the reaction network. Accurate knowledge of the HCl abundance in the interstellar medium requires the calculation of excitation rate coefficients of HCl due to collisions with the most abundant collisional partners. Following the recent calculations of HCl-He, HCl-H₂ and HCl-electron rotational rate coefficients, we report here theoretical calculations of the HCl-H collisional data. Fully quantum time-independent rate coefficients for the collisional excitation of HCl by H are provided for temperature ranging from 10 to 500 K. The strongest collision-induced rotational HCl transitions are those with Δj = 1 and the magnitude of the HCl-H rate coefficients is larger than that of the HCl-H₂ ones. In addition, we also provide rate coefficients for the collisional dissociation of HCl by H, another astrophysically relevant process. Below 300 K, it is found that the destruction of HCl induced by collisions with H is much faster than previously considered in astrochemical models. As a first application, we simulate the excitation of HCl by H₂ and H in typical protostellar shock conditions. We show that hydrogen atoms significantly increase the simulated line intensities, suggesting HCl abundance lower than currently estimated.