Effects of Collisional and Vibrational Velocity on Proton and Deuteron Transfer in the Reaction of HOD+ with CO

Abstract

Reaction of HOD(+) with CO was studied over the collision energy (E(col)) range between 0.18 and 2.87 eV, for HOD(+) in its ground state and with one quantum in each of its vibrational modes: (001)--predominantly OH stretch; (010)--bend, and (100)--predominately OD stretch. In addition to integral cross sections, product recoil velocity distributions were also measured for each initial condition. The dominant reactions are near-thermoneutral proton and deuteron transfer, generating HCO(+) and DCO(+) product ions by a predominantly direct mechanism. The HCO(+) and DCO(+) channels occur with a combined efficiency of 76% for ground state HOD(+) at our lowest E(col), increasing to 94% for E(col) around 0.33 eV, then falling at high E(col) to ~40%. The HCO(+) and DCO(+) channels have a complicated dependence on the HOD(+) vibrational state. Excitation of the OH or OD stretch modes enhances H(+) or D(+) transfer, respectively, and inhibits D(+) or H(+) transfer. Bend excitation preferentially enhances H(+) transfer, with no effect on D(+) transfer. There is no coupling of energy initially in any HOD(+) vibrational mode to recoil velocity of either of the product ions, even at low E(col) where vibrational excitation doubles or triples the energy available to products. The results suggest that transfer of H or D atoms is enhanced if the atom in question has a high vibrational velocity, and that this effect offsets what is otherwise a general inhibition of reactivity by added energy. HOCO(+) + D and DOCO(+) + H products are also observed, but as minor channels despite being barrierless and exoergic. These channels appear to be complex mediated at low E(col), essentially vanish at intermediate E(col), then reappear with a direct reaction mechanism at high E(col).