A combined crossed-beam and ab initio study of the atom-radical reaction dynamics of O(P-3) + C2H5 -> C2H4 + OH: analysis of nascent internal state distributions of the OH product

Abstract

The oxidation reaction dynamics of ethyl radicals (C2H5) in the gas phase are investigated by applying a combination of high-resolution laser induced fluorescence spectroscopy in a crossed-beam configuration and ab initio theoretical calculations. The supersonic atomic oxygen (O(P-3)) and ethyl (C2H5) reactants are produced by photodissociation of NO2 and supersonic. ash pyrolysis of a synthesized precursor (azoethane), respectively. An exothermic channel leading to the C2H5 + OH (X-2 Pi: upsilon '' = 0, 1) products is identified. The nascent rovibrational state distributions of the OH product show substantial bimodal internal excitations consisting of low-and high-N '' components with neither spin-orbit nor Lambda-doublet propensities in the ground and first excited vibrational states. The averaged vibrational population (P-upsilon ''), partitioning with respect to the low-N '' components of the upsilon '' = 0 level, shows a comparable population ratio of P-0 : P-1 = 1 : 1.06. On the basis of comparison between the population analyses using ab initio and prior statistical calculations, the title atom-radical reactive scattering processes are governed by dynamic characteristics. The reaction mechanism can be rationalized by two competing mechanisms: abstraction versus addition. The major low N ''-components can be described in terms of the direct abstraction process responsible for the comparable vibrational populations, while the minor but hot rotational distribution of the high N ''-components implies that some fraction of radical reactants is sampled to proceed through the short-lived addition-complex forming process.