The addition of vinylic radicals to acetylene is an important step contributing to the formation of polycyclic aromatic hydrocarbons in combustion. The overall reaction 3C₂H₂ → C₆H₆ could result in large benzene yields, but without accurate rate parameters validated by experiment, the extent of aromatic ring formation from this pathway is uncertain. The addition of vinyl radicals to acetylene was investigated using time-resolved photoionization time-of-flight mass spectrometry at 500 and 700 K and 5–50 Torr. The formation of C₆H₆ was observed at all conditions, attributed to sequential addition to acetylene followed by cyclization. Vinylacetylene (C₄H₄) was observed with increasing yield from 500 to 700 K, attributed to the β-scission of the thermalized 1,3-butadien-1-yl radical and the chemically activated reaction C₂H₃ + C₂H₂ → C₄H₄ + H. The measured kinetics and product distributions are consistent with a kinetic model constructed using pressure- and temperature-dependent reaction rate coefficients computed from previously reported ab initio calculations. The experiments provide direct measurements of the hypothesized C₄H₅ intermediates and validate predictions of pressure-dependent addition reactions of vinylic radicals to C₂H₂, which are thought to play a key role in soot formation.

中文翻译：

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直接测量由乙炔自由基催化的C6H6的形成，并验证C2H3 + C2H2和C4H5 + C2H2反应的理论速率系数。

向乙炔中添加乙烯基自由基是有助于燃烧中形成多环芳烃的重要步骤。整个反应3C ₂ H ₂ →C ₆ H ₆可能导致苯的大量收率，但如果没有通过实验验证的准确速率参数，则不确定该途径形成的芳环的程度。使用时间分辨的光电离飞行时间质谱在500和700 K以及5-50 Torr下研究了向乙炔中添加乙烯基自由基的过程。在所有条件下均观察到C ₆ H ₆的形成，这归因于顺序添加至乙炔，然后环化。乙烯基乙炔（C ₄ H₄）观察到产率从500 K增加到700 K，这归因于热化的1,3-丁二烯-1-基的β断裂和化学活化的反应C ₂ H ₃ + C ₂ H ₂ →C ₄ H ₄ +H。测得的动力学和产物分布与动力学模型一致，该动力学模型是使用由先前报道的从头算计算得出的依赖于压力和温度的反应速率系数构建的。实验提供了对假设的C ₄ H ₅中间体的直接测量，并验证了乙烯基自由基与C的压力依赖性加成反应的预测₂ H ₂，据认为在烟灰形成中起关键作用。