Study of the Gas-Phase Oxygen–Hydrogen Exchange Reaction of O(³P) + i-C₃H₇ → H(²S) + CH₃COCH₃

Abstract

The gas-phase oxygen-hydrogen exchange reaction dynamics of O((3)P) + i-C3H7 (isopropyl) → H((2)S) + CH3OCH3 (acetone) was first investigated by the vacuum-ultraviolet laser-induced fluorescence (VUV-LIF) spectroscopy in a crossed beam configuration. The nascent H-atom Doppler-profile analysis shows that the average translation energy of the products and the fraction of the total available energy released as the transitional energy were determined to be 33.3 ± 1.64 kcal mol(-1) and 0.38, respectively. With the aid of the CBS-QB3 level of ab initio theory and statistical calculations, it was found that the title reaction is one of the major reaction pathways and proceeds through the formation of dynamical, short-lived addition complexes. On the basis of a systematic comparison with several exchange reactions of hydrocarbon radicals, the large variation in the fractions of translational energy release can be understood in terms of the unique geometrical features of the transition states along the reaction coordinates on the doublet potential energy surfaces.

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

“…6 In the case of the medium transition state, the observed f T value can be attributed to the medium C-H bond length and reverse activation barrier, as shown in the O + iso-propyl reaction. 5 In the case of the title O( 3 P) + ethyl reaction, the observed small f T value can be attributed to both the long C-H bond length (1.85 Å) and the small reverse activation barrier (4.7 kcal mol −1 ), which corresponds to occurrence of the dynamics in the loose transition state.…”

“…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.…”

Probing the kinetic energy-release dynamics of H-atom products from the gas-phase reaction of O(3P) with vinyl radical C2H3

“…This work develops from this lab's recent progress in crossed-beam investigations of the reaction dynamics of O( 3 P) with a series of prototypical hydrocarbon radicals such as allyl (C 3 H 5 ), propargyl (C 3 H 3 ), t-butyl (t-C 4 H 9 ), ethyl (C 2 H 5 ) and iso-propyl (i-C 3 H 7 ). [4][5][6][7][8][9][10][11] All alkyl radicals were produced using a supersonic flash pyrolysis developed by Chen and coworkers. 12 The labile precursor molecules entrained in a molecular beam experienced a very short residence time inside a high-temperature tube, leading to rapid thermal decomposition into clean, jet-cooled radical beams without recombination and/or secondary dissociation.…”