Dynamics of hydrogen atom abstraction in the O{sup {minus}}+CH{sub 4} reaction: Product energy disposal and angular distributions
- Department of Chemistry, University of Rochester, Rochester, New York 14627 (United States)
Energy and angular distributions for the hydrogen abstraction reaction O{sup {minus}}+CH{sub 4}{r_arrow}OH{sup {minus}}+CH{sub 3}, exothermic by 0.26 eV, and a prototype ionic pathway for methane oxidation in hydrocarbon flames have been studied in a crossed molecular beam experiment at collision energies of 0.34, 0.44, and 0.64 eV. At the two lower collision energies, two mechanisms contribute to the differential cross section: In the first, low impact parameter rebound collisions form sharply backward-scattered products, while in the second, larger impact parameter collisions produce a broad distribution of forward scattered products. We suggest that the first group of products is formed by collisions with hydrogen atoms oriented essentially along the relative velocity vector and proceeding through a near-collinear O{hor_ellipsis}H{hor_ellipsis}CH{sub 3} geometry, while the second group corresponds to collisions with one of the three off-axis hydrogens. The products are formed on average with 65{percent} of the total available energy in product internal excitation. The product kinetic energy distribution shows structure that correlates with excitation of the {nu}{sub 2} umbrella bending mode of CH{sub 3}. At the highest collision energy, the product angular distribution shifts entirely to the forward direction, suggesting that the low impact parameter collisions are no longer important in the reactive process. At this energy, the average product internal excitation corresponds to 59{percent} of the total available energy. The data suggest that the majority of product internal excitation resides in the {nu}{sub 2} umbrella bending mode of CH{sub 3}, with OH in its ground vibrational state. {copyright} {ital 1997 American Institute of Physics.}
- OSTI ID:
- 535931
- Journal Information:
- Journal of Chemical Physics, Vol. 106, Issue 14; Other Information: PBD: Apr 1997
- Country of Publication:
- United States
- Language:
- English
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