Branching ratio for O + H+3 forming OH+ + H2 and H2O+ + H

Hillenbrand, Pierre-Michel [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, U.S.A. - Institut fur Kernphysik, Goethe-Universitat, D-60438 Frankfurt, Germany] Ruette, Nathalie de [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, U.S.A.- European Spallation Source ERIC, SE-22100 Lund, Sweden] Urbain, Xavier [UCL] Savin, Daniel W. [Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027, U.S.A.]

The gas-phase reaction of O+H+3 has two exothermic product channels, OH+8 +H2 and H2O++H. In the present study, we analyze experimental data from a merged-beams measurement to derive thermal rate coe_cients resolved by product channel for the temperature range from 10 to 1000 K. Published astrochemical models either ignore the second product channel or apply a temperature-independent branching ratio of 70% vs. 30% for the formation of OH+ 12 + H2 vs. H2O+ + H, respectively, which originates from a single experimental data point measured at 295 K. Our results are consistent with this data point, but show a branching ratio that varies with temperature reaching 58% vs. 42% at 10 K. We provide recommended rate coe_cients for the two product channels for two cases, one where the initial _ne-structure population of the O(3PJ ) reactant is in its J = 2 ground state and the other one where it is in thermal equilibrium.