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Context <p>The H<sub>2</sub>CCCH radical plays a crucial role in combustion chemistry, astrophysical processes, and the formation of complex organic molecules, serving as a key intermediate in the synthesis of polycyclic aromatic hydrocarbons and soot precursors. The reactions of H<sub>2</sub>CCCH with small species are significant for understanding the mechanisms of hydrocarbon transformation in combustion, atmospheric chemistry, and interstellar environments. In the present study, the mechanism and kinetics of the H + H<sub>2</sub>CCCH have been thoroughly characterized. The calculated results indicate that the reaction can proceed via H-addition to the H<sub>2</sub>CCCH carbon chain without an energy barrier, forming the adducts (C<sub>3</sub>H<sub>4</sub>). These intermediates can then undergo H<sub>2</sub>-abstraction or carbon-chain cleavage to create various products, in which PR<sub>1</sub> (<sup>1</sup>HCCCH + H<sub>2</sub>) and PR<sub>4</sub> (H<sub>2</sub>CCC + H<sub>2</sub>) are the main products of the reaction system. Furthermore, the triplet potential surface shows the dominant channel forming the product PR<sub>11</sub> (<sup>3</sup>HCCCH + H<sub>2</sub>). In the low-temperature region, PR<sub>4</sub> is dominant, exhibiting a 70% branching ratio at 400&#xa0;K; at higher temperatures, the PR<sub>11</sub> product prevails, with a 65.7% branching ratio at 2000&#xa0;K. The bimolecular rate constants of the reaction are positively dependent on temperatures but negatively dependent on pressures. The calculated rate constants in this study agree well with the available literature data. The computational results of the H + H<sub>2</sub>CCCH reaction provide profound insights into the theoretical aspects and offer valuable applications for modeling reaction systems involving the propargyl radicals.</p> Methods <p>The B3LYP and CCSD(T) methods, combined with the aug-cc-pVnZ (<i>n</i> = T, Q, 5) basis sets, were employed to optimize structures and calculate single-point energies for all species involved in the reaction. The temperature range (200 – 2000&#xa0;K) and pressure range (0 – 7600&#xa0;Torr) were used to calculate the bimolecular rate constants for the dominant reaction pathways. The TST, VRC-TST, and RRKM models, with the small curvature tunneling correction, were employed for the kinetic calculations.</p>

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Investigation of product formation in the H + H2C = C = CH reaction: a comparison of experimental and theoretical kinetics

  • 期刊论文

  • 发表日期：

    2025年3月8日

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  • Hoang T. T. Trang,
  • Nghiem T. Thuong,
  • Tien V. Pham

摘要

Context

The H2CCCH radical plays a crucial role in combustion chemistry, astrophysical processes, and the formation of complex organic molecules, serving as a key intermediate in the synthesis of polycyclic aromatic hydrocarbons and soot precursors. The reactions of H2CCCH with small species are significant for understanding the mechanisms of hydrocarbon transformation in combustion, atmospheric chemistry, and interstellar environments. In the present study, the mechanism and kinetics of the H + H2CCCH have been thoroughly characterized. The calculated results indicate that the reaction can proceed via H-addition to the H2CCCH carbon chain without an energy barrier, forming the adducts (C3H4). These intermediates can then undergo H2-abstraction or carbon-chain cleavage to create various products, in which PR1 (1HCCCH + H2) and PR4 (H2CCC + H2) are the main products of the reaction system. Furthermore, the triplet potential surface shows the dominant channel forming the product PR11 (3HCCCH + H2). In the low-temperature region, PR4 is dominant, exhibiting a 70% branching ratio at 400 K; at higher temperatures, the PR11 product prevails, with a 65.7% branching ratio at 2000 K. The bimolecular rate constants of the reaction are positively dependent on temperatures but negatively dependent on pressures. The calculated rate constants in this study agree well with the available literature data. The computational results of the H + H2CCCH reaction provide profound insights into the theoretical aspects and offer valuable applications for modeling reaction systems involving the propargyl radicals.

Methods

The B3LYP and CCSD(T) methods, combined with the aug-cc-pVnZ (n = T, Q, 5) basis sets, were employed to optimize structures and calculate single-point energies for all species involved in the reaction. The temperature range (200 – 2000 K) and pressure range (0 – 7600 Torr) were used to calculate the bimolecular rate constants for the dominant reaction pathways. The TST, VRC-TST, and RRKM models, with the small curvature tunneling correction, were employed for the kinetic calculations.