A gas-phase crossed-beam study of OH produced in the radical–radical reaction of O(3P) with iso-propyl radical (CH3)2CH

Abstract

The gas-phase radical-radical reaction dynamics of ground-state atomic oxygen [O((3)P)] with iso-propyl radicals, (CH(3))(2)CH, were investigated by applying a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. The nascent distributions of OH (X(2)Π: υ'' = 0) from the major reaction channel O((3)P) + (CH(3))(2)CH → C(3)H(6) (propene) + OH showed substantial internal excitations with a bimodal feature of low- and high-N'' components with neither spin-orbit nor Λ-doublet propensities. Unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, on the basis of the population analysis and comparison with the statistical theory, the title reaction can be described in terms of two competing mechanisms at the molecular level: direct abstraction process and indirect short-lived addition-complex-forming process with a ratio of 1.25 : 1.

A Gas-Phase Investigation of Oxygen-Hydrogen Exchange Reaction of O(3P) + C2H5→ H(2S) + C2H4O

“…After considering the barrier height and reaction exothermicity along the reaction coordinate, the title reaction is, in fact, predicted to be a major channel, which is consistent with the gas-phase kinetic experiments. [5][6][7][8][9][10][11] Statistical Analyses and Reaction Dynamics. The partitioning of the energy into the H products and the microscopic kinetic rate constants were derived using the aforementioned ab initio calculations.…”

“…The crossed-beam apparatus used in this study was made in-house and has been described in detail elsewhere. 3,[5][6][7][8][9][10][11] In brief, a pulsed O( 3 P) radical beam was produced by irradiating 2 atm of He (ultra-high-purity helium: 99.999%) seeded with 12% NO 2 (99.5%, MG Industries) with 30 mJ pulses from a 355 nm Nd:YAG laser beam (Continuum Surelite II-10) near the throat of the supersonic expansion. A second C 2 H 5 radical beam was prepared by supersonic flash pyrolysis of the precursor, azoethane (C 2 H 5 -N=N-C 2 H 5 ), synthesized using the method of Renaud and Leitch.…”

“…4 By adopting the supersonic flash pyrolysis source, a series of combined crossed-beam and theoretical studies of the prototypal oxidation reactions of both π-conjugated hydrocarbon radicals such as allyl (C 3 H 5 ), propargyl (C 3 H 3 ), vinyl (C 2 H 3 ), and saturated hydrocarbon radicals such as t-butyl (t-C 4 H 9 ), ethyl (C 2 H 5 ), and iso-propyl (i-C 3 H 7 ) have recently been executed in our laboratory. [5][6][7][8][9][10][11] The analyses of the energy distributions of the nascent reaction products have demonstrated extraordinary reactivity and mechanistic characteristics, which have not previously been observed in the reactions of O( 3 P) + closed-shell hydrocarbon molecules. 12,13 Based on the authors' theoretical calculations, Leonori et al also studied the oxidation reaction of allyl radicals using a universal crossed-beam apparatus.…”

Analysis of Nascent Rotational Energy Distributions and Reaction Mechanisms of the Gas‐Phase Radical–Radical Reaction O(3P)+(CH3)2CH→C3H6+OH

“…Calculations: The density functional method and the complete basis set (CBS) model were employed to obtain the reaction mechanisms and pathways as well as the kinetic and dynamic characteristics of the lowest doublet potential-energy surfaces necessary to interpret the experimental data. [36] The geometries of local minima and transition states along the reaction coordinates were optimized at the hybrid density functional B3LYP level with 6-311G(d) and 6-311 + G(3df,2p) basis sets as initial guesses. [37][38][39][40][41] Vibrational frequencies of the geometries were computed to characterize stationary points and zero-point energy corrections with a scaling factor of 0.98.…”

Crossed beam study of the atom-radical reaction of ground state carbon atoms (C(3P)) with the vinyl radical (C2H3(X2A′))

“…Later, Casavecchia et al disseminated the results of the crossed beam reactions of ground and excited state oxygen atoms with methyl (CH 3 ) 17,18 and allyl radicals (C 3 H 5 ) 19,20 at collision energies of 55.9 kJ mol À1 and 73.0 kJ mol À1 , respectively. Further, Choi et al conducted a series of experiments with the main emphasis focusing on the reactions of ground state atomic oxygen atoms (O( 3 P)) with hydrocarbon radicals allyl, t-butyl, ethyl, propyl, and propargyl, [21][22][23][24][25][26] Luntz et al revised selected systems. 27,28 The reactions investigated by Choi et al followed similar patterns, i.e.…”