Why HOC⁺ is detectable in interstellar clouds: The rate of the reaction between HOC⁺ and H₂

The recent confirmation by Ziurys and Apponi of the detection of HOC⁺ toward Sgr B2 (OH), and their identification of the ion in Orion-KL and several other sources show that HOC⁺ is far more abundant than predicted by previous ion-molecule models. In these models, the reaction HOC⁺ + H² → HCO⁺ + H₂ is assumed to rapidly destroy HOC⁺, based on the results of a prior calculation. We have recalculated the rate of this reaction as a function of temperature using a new ab initio potential surface and a phase space approach to the dynamics which includes tunneling. The newly calculated rate is small (≤1 × 10^-10 cm³ s^-1) at temperatures under 100 K.