The chemical dynamics of the reactions of O(3P) with saturated hydrocarbons. I. Experiment

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Abstract
Molecular beam‐laser induced fluorescence experiments have probed the nascent internal state distributions and excitation functions of OH formed in the technologically important reactions O(3P)+RH→OH+R⋅. RH is a saturated hydrocarbon and R⋅ is an alkyl radical. A variety of RH have been investigated corresponding to abstraction of primary, secondary, and tertiary hydrogens. The OH rotational state distribution is nearly identical for all RH and decrease rapidly from its peak at the lowest rotational level. This demonstrates that reaction occurs when O(3P) is collinear to a C–H bond in the hydrocarbons. The vibrational state distribution of OH depends markedly on the type of hydrogen abstracted, with vibrational excitation increasing dramatically across the series primary to secondary to tertiary. This is interpreted as a shift from a repulsive towards a more attractive surface across the series. Partitioning into the OH spin doublets shows that these reactions are midway between the adiabatic and diabatic limits with respect to the spin–orbit surfaces. Excitation functions measure the dynamic thresholds, and are in good agreement with activation energies obtained from thermal rate constants. The excitation functions for v=1 OH exhibit a sharp decrease at energies considerably above threshold. This suggests that excitation of internal modes of R⋅ occurs only at high collisions energies. All of these results are interpreted qualitatively in terms of a simple, but general, triatomic model for the interaction of O(3P) with RH, i.e., where R⋅ can be considered a structureless particle.