Why HOC+ is detectable in interstellar clouds: The rate of the reaction between HOC+ and H-2

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+ + H-2 --> HCO+ + H-2 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 (less than or equal to 1 x 10(-10) cm(3) s(-1)) under 100 K.