Product branching ratios of the reaction of co with H+3 and H2D+

Abstract

The reaction of CO with H+3 and H2D + has been studied to investigate thermal rate coefficients and product branching ratios in the temperature range [20, 350] K, by using a direct ab initio molecular dynamics method. In trajectory simulations, the energies and forces are calculated using a scaling all correlation second-order Mφller-Plesset perturbation theory (SAC-MP2) method with the correlation consistent polarized valence triplet-zeta basis (cc-pVTZ). Results show that total thermal rate coefficients for both the CO + H+3and the CO + H2D+ reactions have a weakly positive temperature dependence. At room temperature, the rate coefficients are predicted to be (1.42 ± 0.03) × 10-9 cm3 molecule -1 s-1 with a product branching ratio of [HOC +]/[HCO+] = 0.36 ± 0.01 for the CO + H+3 reaction, and (1.26 0.03) × 10-9 cm3 molecule-1 s-1 with the product branching ratios: 0.37 0.01 (([HOC+] + [DOC+])/([HCO+] + [DOC +])), 0.54 ± 0.02 ([DCO+]/[HCO+]), and 0.49 0.02 ([DOC+]/[HOC+]) for CO + H2D +. The product branching ratios have a noticeable temperature dependence as well as a pronounced isotopic effect for the H/DOC+ product channel. © 2009. The American Astronomical Society. All rights reserved.