Crossed-beam investigation of O(³P) + C₂H₅ → C₂H₄ + OH

The reaction dynamics of ground-state atomic oxygen [O(³P)] with an ethyl radical (C2H5) in the gas phase was investigated using high-resolution laser spectroscopy in a crossed-beam configuration. An exothermic channel of O(³P) + C₂H₅ → C₂H₄ + OH was identified, and the nascent distributions of OH (X ²π: ν″? 0, 1) showed significant internal excitations with an unusual bimodal feature of low and high rotational N″-components with neither spin-orbit nor λ-doublet propensities. On the basis of the ab initio and statistical calculations, the reaction mechanism can be rationalized by two competing mechanisms: abstraction vs addition. The low N″-components with significant vibrational excitation can be described in terms of the direct abstraction process as a major channel. The extraordinarily hot rotational distribution of high N″-components implies that a portion of the fraction proceeds through the indirect short-lived addition-complex forming process. From the comparative analysis of the reactions of O(³P) + several hydrocarbon molecules and radicals, the reactivity and mechanistic characteristics of the title reaction are discussed.