Reaction of O2+(X 2Πg) with H2 , D2 , and HD: Guided ion beam studies, MO correlations, and statistical theory calculations

Abstract

Absolute cross sections are measured for the reactions of O2+(X 2Πg) with H2 , D2 , and HD from thermal energies to over 4 eV. The OH++OH, HO2++H, O++H2O, and H2O++O product channels (and the corresponding isotopic analogs) are observed, although H2++O2 is not. While the first three products appear at their thermodynamic thresholds, formation of H2O++O, the least endothermic channel, exhibits a barrier to reaction. In the HD system, the DO2+ product ion is strongly favored over the HO2+ product. Results for internally excited O2+ reactants, probably the a 4Πu state, are also presented. Analysis of the excitation functions, molecular orbital arguments, and statistical kinetic theories are used to understand the mechanisms and dynamics of this reaction. It is shown that the inefficiency of the O+ product channel is due to spin and symmetry constraints. The other three product channels proceed through a long-lived intermediate, but formation of this intermediate from reactants requires surmounting a barrier measured to be 1.1±0.1 eV. The intramolecular isotope effects are shown to be due to statistical and dynamic effects.