A combined crossed-beam and theoretical study of the reaction dynamics of O(3P) C2H3 → C2H2 OH: Analysis of the nascent OH products with the preferential population of the Π(A′) component

Min Jin Park, Su Chan Jang, Jong-Ho Choi

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Abstract

The gas-phase reaction dynamics of ground-state atomic oxygen O( 3P) from the photo-dissociation of NO2 with vinyl radicals C2H3 from the supersonic flash pyrolysis of vinyl iodide, C2H3I has been investigated using a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. Unlike the previous gas-phase bulk kinetic experiments by Baulch J. Phys. Chem. Ref. Data 34, 757 (2005)10.1063/1.1748524, a new exothermic channel of O(3P) C 2H3 → C2H2 OH (X 2Π: υ″ 0) has been identified for the first time, and the population analysis shows bimodal nascent rotational distributions of OH products with low- and high-N″ components with a ratio of 2.4:1. No spin-orbit propensities were observed, and the averaged ratios of Π(A )Π(A″) were determined to be 1.66 ± 0.27. On the basis of computations at the CBS-QB3 theory level and comparison with prior theory, the microscopic mechanisms responsible for the nascent populations can be understood in terms of two competing dynamical pathways: a direct abstraction process in the low-N″ regime as the major pathway and an addition-complex forming process in the high-N″ regime as the minor pathway. Particularly, during the bond cleavage process of the weakly bound van der Waals complex C2H2-OH, the characteristic pathway from the low dihedral-angle geometry was consistent with the observed preferential population of the Π(A′) component in the nascent OH products. A molecular-level discussion of the reactivity, mechanism, and dynamical features of the title reaction are presented together with a comparison to gas-phase oxidation reactions of a series of prototypical hydrocarbon radicals.

Original languageEnglish
Article number204311
JournalJournal of Chemical Physics
Volume137
Issue number20
DOIs
Publication statusPublished - 2012 Nov 28

Fingerprint

Gases
vapor phases
products
vinyl radical
Photodissociation
Fluorescence spectroscopy
Dihedral angle
Hydrocarbons
photodissociation
laser induced fluorescence
Ground state
iodides
pyrolysis
flash
dihedral angle
cleavage
Orbits
Pyrolysis
reactivity
hydrocarbons

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

Cite this

@article{43088c9d6fd3455eb6d43543358e8553,
title = "A combined crossed-beam and theoretical study of the reaction dynamics of O(3P) C2H3 → C2H2 OH: Analysis of the nascent OH products with the preferential population of the Π(A′) component",
abstract = "The gas-phase reaction dynamics of ground-state atomic oxygen O( 3P) from the photo-dissociation of NO2 with vinyl radicals C2H3 from the supersonic flash pyrolysis of vinyl iodide, C2H3I has been investigated using a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. Unlike the previous gas-phase bulk kinetic experiments by Baulch J. Phys. Chem. Ref. Data 34, 757 (2005)10.1063/1.1748524, a new exothermic channel of O(3P) C 2H3 → C2H2 OH (X 2Π: υ″ 0) has been identified for the first time, and the population analysis shows bimodal nascent rotational distributions of OH products with low- and high-N″ components with a ratio of 2.4:1. No spin-orbit propensities were observed, and the averaged ratios of Π(A ′)Π(A″) were determined to be 1.66 ± 0.27. On the basis of computations at the CBS-QB3 theory level and comparison with prior theory, the microscopic mechanisms responsible for the nascent populations can be understood in terms of two competing dynamical pathways: a direct abstraction process in the low-N″ regime as the major pathway and an addition-complex forming process in the high-N″ regime as the minor pathway. Particularly, during the bond cleavage process of the weakly bound van der Waals complex C2H2-OH, the characteristic pathway from the low dihedral-angle geometry was consistent with the observed preferential population of the Π(A′) component in the nascent OH products. A molecular-level discussion of the reactivity, mechanism, and dynamical features of the title reaction are presented together with a comparison to gas-phase oxidation reactions of a series of prototypical hydrocarbon radicals.",
author = "Park, {Min Jin} and Jang, {Su Chan} and Jong-Ho Choi",
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AU - Park, Min Jin

AU - Jang, Su Chan

AU - Choi, Jong-Ho

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AB - The gas-phase reaction dynamics of ground-state atomic oxygen O( 3P) from the photo-dissociation of NO2 with vinyl radicals C2H3 from the supersonic flash pyrolysis of vinyl iodide, C2H3I has been investigated using a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. Unlike the previous gas-phase bulk kinetic experiments by Baulch J. Phys. Chem. Ref. Data 34, 757 (2005)10.1063/1.1748524, a new exothermic channel of O(3P) C 2H3 → C2H2 OH (X 2Π: υ″ 0) has been identified for the first time, and the population analysis shows bimodal nascent rotational distributions of OH products with low- and high-N″ components with a ratio of 2.4:1. No spin-orbit propensities were observed, and the averaged ratios of Π(A ′)Π(A″) were determined to be 1.66 ± 0.27. On the basis of computations at the CBS-QB3 theory level and comparison with prior theory, the microscopic mechanisms responsible for the nascent populations can be understood in terms of two competing dynamical pathways: a direct abstraction process in the low-N″ regime as the major pathway and an addition-complex forming process in the high-N″ regime as the minor pathway. Particularly, during the bond cleavage process of the weakly bound van der Waals complex C2H2-OH, the characteristic pathway from the low dihedral-angle geometry was consistent with the observed preferential population of the Π(A′) component in the nascent OH products. A molecular-level discussion of the reactivity, mechanism, and dynamical features of the title reaction are presented together with a comparison to gas-phase oxidation reactions of a series of prototypical hydrocarbon radicals.

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