title: A combined crossed-beam and ab initio study of the atom-radical reaction dynamics of O((3)P) + C(2)H(5)--> C(2)H(4) + OH: analysis of nascent internal state distributions of the OH product.
abstract: The oxidation reaction dynamics of ethyl radicals (C(2)H(5)) 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((3)P)) and ethyl (C(2)H(5)) reactants are produced by photodissociation of NO(2) and supersonic flash pyrolysis of a synthesized precursor (azoethane), respectively. An exothermic channel leading to the C(2)H(5) + 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)ratioP(1) = 1 ratio 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.
authors.affiliation: Department of Chemistry and Center for Electro- & Photo-Responsive Molecules, Korea University, 1, Anam-dong, Seoul 136-701, Korea.
authors.forename: Yong-Pal
authors.initials: YP
authors.lastname: Park
authors.forename: Kyoo-Weon
authors.initials: KW
authors.lastname: Kang
authors.forename: Se-Hee
authors.initials: SH
authors.lastname: Jung
authors.forename: Jong-Ho
authors.initials: JH
authors.lastname: Choi