Formation of HOCO+ in magnetohydrodynamical shocks propagating in dark interstellar clouds

Abstract

The formation and destruction of HOCO⁺ in dark interstellar clouds are investigated. In cold gas at equilibrium, the main formation process may be HCO⁺(OH, H) HOCO⁺ and not H⁺₃(CO₂, H₂)HOCO⁺ as originally suggested. In MHD shocks, the endothermic reaction HCO⁺(O₂, O) HOCO⁺ could be driven by the ion–neutral drift velocity, leading to a high value of the HOCO⁺/HCO⁺ abundance ratio. The recent detection of HOCO⁺ in the galactic center may be a signature of MHD shock propagation.