## 摘要

The unimolecular decomposition of the C_{6}H_{5} radical has been studied by ab initio molecular orbital and statistical-theory calculations. Three low-energy decomposition channels, including the commonly assumed decyclization/fragmentation process yielding n-C_{4}H_{3} + C_{2}H_{2}, have been identified. With a modified Gaussian-2 method of Mebel et al. (ref 17), the energy barrier for the decyclization of C_{6}H_{5} was calculated to be 66.5 kcal/mol with the corresponding recyclization energy of 5.6 kcal/mol. The two open-chain 1-dehydrohexa-1,3-dien-5-yne radicals (with HCCH cis and trans structures) may undergo further fragmentation reactions producing n-C_{4}H_{3} + C_{2}H_{2} and l-C_{6}H_{4} (1,5-hexadiyn-3-ene) + H with the predicted barriers of 44.0 and 36.1 kcal/mol, respectively. The dominant decomposition channel of C_{6}H_{5} was found to take place barrierlessly by C-H breaking, producing o-C_{6}H_{4} (o-benzyne) + H with the predicted endothermicity of 76.0 kcal/mol. RRKM calculations have been carried out for the production of n-C_{4}H_{3} + C_{2}H_{2}, l-C_{6}H_{4} + H, and o-C_{6}H_{4} + H with the coupled multichannel mechanism, which includes the reversible decyclization/recyclization reactions. The results of the calculations indicate that at T < 1500 K o-C_{6}H_{4} is the major product of the decomposition reaction. Above 1500 K, the formation of l-C_{6}H_{4} becomes competitive with its cyclic isomer. However, the formation of the commonly assumed n-C_{4}H_{3} + C_{2}H_{2} products was found to be least competitive. Rate constants for all three product channels from C_{6}H_{5} as well as those from the bimolecular reaction of n-C_{4}H_{3} with C_{2}H_{2} producing C_{6}H_{5}, o-C_{6}H_{4} + H, and l-C_{6}H_{4} + H have been calculated as functions of temperature and pressure for practical applications.

原文 | English |
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頁（從 - 到） | 6790-6797 |

頁數 | 8 |

期刊 | Journal of Physical Chemistry A |

卷 | 101 |

發行號 | 36 |

DOIs | |

出版狀態 | Published - 4 9月 1997 |