Premium
Analysis of Nascent Rotational Energy Distributions and Reaction Mechanisms of the Gas‐Phase Radical–Radical Reaction O( 3 P)+(CH 3 ) 2 CH→C 3 H 6 +OH
Author(s) -
Park MinJin,
Kang KyooWeon,
Choi JongHo
Publication year - 2012
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201100962
Subject(s) - chemistry , radical , crossed molecular beam , reactivity (psychology) , ground state , photodissociation , molecular beam , potential energy surface , population , photochemistry , reaction dynamics , reaction mechanism , photoionization , analytical chemistry (journal) , ab initio , atomic physics , molecule , ionization , medicine , physics , alternative medicine , demography , organic chemistry , pathology , sociology , catalysis , ion , biochemistry , chromatography
This paper reports on the gas‐phase radical–radical dynamics of the reaction of ground‐state atomic oxygen [O( 3 P), from the photodissociation of NO 2 ] with secondary isopropyl radicals [(CH 3 ) 2 CH, from the supersonic flash pyrolysis of isopropyl bromide]. The major reaction channel, O( 3 P)+(CH 3 ) 2 CH→C 3 H 6 (propene)+OH, is examined by high‐resolution laser‐induced fluorescence spectroscopy in crossed‐beam configuration. Population analysis shows bimodal nascent rotational distributions of OH (X 2 Π) products with low‐ and high‐ N ′′ components in a ratio of 1.25:1. No significant spin–orbit or Λ‐doublet propensities are exhibited in the ground vibrational state. Ab initio computations at the CBS‐QB3 theory level and comparison with prior theory show that the statistical method is not suitable for describing the main reaction channel at the molecular level. Two competing mechanisms are predicted to exist on the lowest doublet potential‐energy surface: direct abstraction, giving the dominant low‐ N ′′ components, and formation of short‐lived addition complexes that result in hot rotational distributions, giving the high‐ N ′′ components. The observed competing mechanisms contrast with previous bulk kinetic experiments conducted in a fast‐flow system with photoionization mass spectrometry, which suggested a single abstraction pathway. In addition, comparison of the reactions of O( 3 P) with primary and tertiary hydrocarbon radicals allows molecular‐level discussion of the reactivity and mechanism of the title reaction.