Crossed-Beam Investigation of O(P-3) + C2H5 -> C2H4 + OH

Abstract

The reaction dynamics of ground-state atomic oxygen [O(P-3)] 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(P-3) + C2H5 -> C2H4 + OH was identified, and the nascent distributions of OH (X (2)Pi: nu '' = 0, 1) showed significant internal excitations with an unusual bimodal feature of low and high rotational N ''-components with neither spin-orbit nor A-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(P-3) + several hydrocarbon molecules and radicals, the reactivity and mechanistic characteristics of the title reaction are discussed.