Atom-radical reaction dynamics of O(3P)+C3H5→C3H4+OH: Nascent rovibrational state distributions of product OH

Abstract

The reaction dynamics of ground-state atomic oxygen ͓O( 3 P)͔ with allyl radicals (C 3 H 5 ) has been investigated by applying a combination of crossed beams and laser induced fluorescence techniques. The reactants O( 3 P) and C 3 H 5 were produced by the photodissociation of NO 2 and the supersonic flash pyrolysis of precursor allyl iodide, respectively. A new exothermic channel of O( 3 P) ϩC 3 H 5 →C 3 H 4 ϩOH was observed and the nascent internal state distributions of the product OH (X 2 ⌸:Љϭ0,1) showed substantial bimodal internal excitations of the low-and high-NЉ components without ⌳-doublet and spin-orbit propensities in the ground and first excited vibrational states. With the aid of the CBS-QB3 level of ab initio theory and Rice-Ramsperger-Kassel-Marcus calculations, it is predicted that on the lowest doublet potential energy surface the major reaction channel of O( 3 P) with C 3 H 5 is the formation of acrolein (CH 2 CHCHO)ϩH, which is consistent with the previous bulk kinetic experiments performed by Gutman et al. ͓J. Phys. Chem. 94, 3652 ͑1990͔͒. The counterpart C 3 H 4 of the probed OH product in the title reaction is calculated to be allene after taking into account the factors of reaction enthalpy, barrier height and the number of intermediates involved along the reaction pathway. On the basis of population analyses and comparison with prior calculations, the statistical picture is not suitable to describe the reactive atom-radical scattering processes, and the dynamics of the title reaction is believed to proceed through two competing dynamical pathways. The major low NЉ-components with significant vibrational excitation may be described by the direct abstraction process, while the minor but extraordinarily hot rotational distribution of high NЉ-components implies that some fraction of reactants is sampled to proceed through the indirect short-lived addition-complex forming process.

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

“…Experimental Studies: The lab-made crossed-beam apparatus for investigating gas-phase reaction dynamics has been described in detail elsewhere. [1,[5][6][7][8][9][10][11][12][13][14][15][16][17] It consists of two radical-source chambers, each pumped by a 6-inch (1400 L s À1 ) baffled diffusion pump, and a scattering chamber, pumped by a 10-inch (3000 L s À1 ) baffled diffusion pump. The average base pressure in the scattering chamber was kept below 2.0 10 À6 Torr.…”

“…Similar results were reported in investigations of H-atom abstraction during reactions of O( 3 P) with ethyl and tert-butyl radicals, where the absence of activation barriers was also attributed to small CÀH BDEs (36.2 and 35.5 kcal mol À1 , respectively) and high exothermicities (DH = À67.3 and À67.2 kcal mol À1 , respectively). [7,13,16] Note that for the main reaction (1), H-atom abstraction from the central C(2)ÀH bond was not considered, since unfavourable endothermic reactions were predicted to lead to OH + 1 C(CH 3 ) 2 and OH + 3 C(CH 3 ) 2 (DH = 1.6 and 3.5 kcal mol À1 , respectively).…”

“…It builds on previous gas-phase crossed-beam studies. [5][6][7][8][9][10][11][12][13][14][15][16][17] Radical-radical reaction dynamics were investigated as part of ongoing efforts to elucidate the mechanistic and dynamic attributes of the reactions of O( 3 P) with a series of prototypal alkyl radicals, such as allyl, propargyl, tert-butyl (t-C 4 H 9 ), and vinyl, and to identify the general principles that determine their reactivity and mechanisms. Some hydrocarbon species showed intrinsic stability due to resonance stabilization or hyperconjugation.…”

Primary photodissociation pathways of epichlorohydrin and analysis of the C–C bond fission channels from an O(P3)+allyl radical intermediate

“…[1][2][3][4][5][6][7][8][9][10][11] The complexity of the competition between bond fission and isomerization pathways is surprising for such a small system, composed of only four heavy atoms and five hydrogen atoms. Previous studies have sought to probe the product branching and dynamics of this reaction.…”

Adventures on the C3H5O potential energy surface: OH + propyne, OH + allene and related reactions

“…Choi and co-workers [4][5][6] studied the reaction of O( 3 P) with the allyl radical using CBS-Q and CBS-QB3 levels of theory. Raman et al [7] created the CH 2 CCH 2 OH intermediate photolytically, and observed bimolecular products; they used G3//B3LYP electronic structure calculations to rationalize their findings.…”