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Published May 15, 1993 | Published
Journal Article Open

Reaction of O_2 ^+(X ^2Π_g) with H_2 , D_2 , and HD: Guided ion beam studies, MO correlations, and statistical theory calculations

Abstract

Absolute cross sections are measured for the reactions of O_2 ^+(X ^2Π_g) with H_2 , D_2 , and HD from thermal energies to over 4 eV. The OH^+ + OH, HO_2^+ + H, O^+ + H_2O, and H_2O^+ + O product channels (and the corresponding isotopic analogs) are observed, although H_2^+ + O_2 is not. While the first three products appear at their thermodynamic thresholds, formation of H_2O^+ + O, the least endothermic channel, exhibits a barrier to reaction. In the HD system, the DO_2^ + product ion is strongly favored over the HO^2^+ product. Results for internally excited O_2^+ reactants, probably the a  ^4Π_u 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.

Additional Information

© 1993 American Institute of Physics. (Received 8 January 1993; accepted 8 February 1993) This work is supported by the National Science Foundation, Grant No. CHE-9221241. P.B.A. also thanks P. A. M. van Koppen for useful conversations regarding phase space theory.

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