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

The reaction dynamics of ground-state atomic oxygen [O((3)P)] with an ethyl radical (C(2)H(5)) in the gas phase was investigated using high-resolution laser spectroscopy in a crossed-beam configuration. An exothermic channel of O((3)P) + C(2)H(5) --> C(2)H(4) + OH was identified, and the nascent distributions of OH (X (2)Pi: upsilon'' = 0, 1) showed significant internal excitations with an unusual bimodal feature of low and high rotational N''-components with neither spin-orbit nor Lambda-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((3)P) + several hydrocarbon molecules and radicals, the reactivity and mechanistic characteristics of the title reaction are discussed.