Dataset Information

Exploring the Chemical Dynamics of Phenylethynyl Radical (C₆H₅CC; X²A₁) Reactions with Allene (H₂CCCH₂; X¹A₁) and Methylacetylene (CH₃CCH; X¹A₁).

ABSTRACT: The bimolecular gas-phase reactions of the phenylethynyl radical (C₆H₅CC, X²A₁) with allene (H₂CCCH₂), allene-d₄ (D₂CCCD₂), and methylacetylene (CH₃CCH) were studied under single-collision conditions utilizing the crossed molecular beams technique and merged with electronic structure and statistical calculations. The phenylethynyl radical was found to add without an entrance barrier to the C1 carbon of the allene and methylacetylene reactants, resulting in doublet C₁₁H₉ collision complexes with lifetimes longer than their rotational periods. These intermediates underwent unimolecular decomposition via atomic hydrogen loss through tight exit transition states in facile radical addition─hydrogen atom elimination mechanisms forming predominantly 3,4-pentadien-1-yn-1-ylbenzene (C₆H₅CCCHCCH₂) and 1-phenyl-1,3-pentadiyne (C₆H₅CCCCCH₃) in overall exoergic reactions (-110 kJ mol^-1 and -130 kJ mol^-1) for the phenylethynyl-allene and phenylethynyl-methylacetylene systems, respectively. These barrierless reaction mechanisms mirror those of the ethynyl radical (C₂H, X²Σ⁺) with allene and methylacetylene forming predominantly ethynylallene (HCCCHCCH₂) and methyldiacetylene (HCCCCCH₃), respectively, suggesting that in the aforementioned reactions the phenyl group acts as a spectator. These molecular mass growth processes are accessible in low-temperature environments such as cold molecular clouds (TMC-1) or Saturn's moon Titan, efficiently incorporating a benzene ring into unsaturated hydrocarbons.

SUBMITTER: Goettl SJ

PROVIDER: S-EPMC10350955 | biostudies-literature | 2023 Jul

REPOSITORIES: biostudies-literature

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Publications

Exploring the Chemical Dynamics of Phenylethynyl Radical (C6H5CC; X2A1) Reactions with Allene (H2CCCH2; X1A1) and Methylacetylene (CH3CCH; X1A1).

Goettl Shane J SJ Yang Zhenghai Z Kollotzek Siegfried S Paul Dababrata D Kaiser Ralf I RI Somani Ankit A Portela-Gonzalez Adrian A Sander Wolfram W Nikolayev Anatoliy A AA Azyazov Valeriy N VN Mebel Alexander M AM

The journal of physical chemistry. A 20230704 27

The bimolecular gas-phase reactions of the phenylethynyl radical (C6H5CC, X2A1) with allene (H2CCCH2), allene-d4 (D2CCCD2), and methylacetylene (CH3CCH) were studied under single-collision conditions utilizing the crossed molecular beams technique and merged with electronic structure and statistical calculations. The phenylethynyl radical was found to add without an entrance barri ...[more]

PMID: 37401904

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Project description:The reaction of excited nitrogen atoms N(2D) with CH3CCH (methylacetylene) was investigated under single-collision conditions by the crossed molecular beams (CMB) scattering method with mass spectrometric detection and time-of-flight analysis at the collision energy (Ec) of 31.0 kJ/mol. Synergistic electronic structure calculations of the doublet potential energy surface (PES) were performed to assist the interpretation of the experimental results and characterize the overall reaction micromechanism. Theoretically, the reaction is found to proceed via a barrierless addition of N(2D) to the carbon-carbon triple bond of CH3CCH and an insertion of N(2D) into the CH bond of the methyl group, followed by the formation of cyclic and linear intermediates that can undergo H, CH3, and C2H elimination or isomerize to other intermediates before unimolecularly decaying to a variety of products. Kinetic calculations for addition and insertion mechanisms and statistical (Rice-Ramsperger-Kassel-Marcus) computations of product branching fractions (BFs) on the theoretical PES were performed at different values of total energy, including the one corresponding to the temperature (175 K) of Titan's stratosphere and that of the CMB experiment. Up to 14 competing product channels were statistically predicted, with the main ones, at Ec = 31.0 kJ/mol, being the formation of CH2NH (methanimine) + C2H (ethylidyne) (BF = 0.41), c-C(N)CH + CH3 (BF = 0.32), CH2CHCN (acrylonitrile) + H (BF = 0.12), and c-CH2C(N)CH + H (BF = 0.04). Of the 14 possible channels, seven correspond to H displacement channels of different exothermicity, for a total H channel BF of ∼0.25 at Ec = 31.0 kJ/mol. Experimentally, dynamical information could only be obtained about the overall H channels. In particular, the experiment corroborates the formation of acrylonitrile + H, which is the most exothermic of all 14 reaction channels and is theoretically calculated to be the dominant H-forming channel (BF = 0.12). The products containing a novel C-N bond could be potential precursors to form other nitriles (C2N2, C3N) or more complex organic species containing N atoms in planetary atmospheres, such as those of Titan and Pluto. Overall, the results are expected to have a potentially significant impact on the understanding of the gas-phase chemistry of Titan's atmosphere and the modeling of that atmosphere.

Dataset Information

Exploring the Chemical Dynamics of Phenylethynyl Radical (C₆H₅CC; X²A₁) Reactions with Allene (H₂CCCH₂; X¹A₁) and Methylacetylene (CH₃CCH; X¹A₁).

Publications

Exploring the Chemical Dynamics of Phenylethynyl Radical (C<sub>6</sub>H<sub>5</sub>CC; X<sup>2</sup>A<sub>1</sub>) Reactions with Allene (H<sub>2</sub>CCCH<sub>2</sub>; X<sup>1</sup>A<sub>1</sub>) and Methylacetylene (CH<sub>3</sub>CCH; X<sup>1</sup>A<sub>1</sub>).

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