Research Center for Chemical Kinetics, Department of Chemistry, The Catholic University of America, Washington, DC 20064, USA.
J Phys Chem A. 2011 Aug 11;115(31):8616-22. doi: 10.1021/jp204012w. Epub 2011 Jul 20.
The kinetics of the self-reaction of cyclohexyl radicals was studied by laser photolysis/photoionization mass spectroscopy. Overall rate constants were obtained in direct real-time experiments in the temperature region 303-520 K and at bath gas (helium with up to 5% of radical precursors) densities (3.00-12.0) × 10(16) molecules cm(-3). Cyclohexyl radicals were produced by a combination of the 193 nm photolysis of oxalyl chloride ((CClO)(2)) with the subsequent fast reaction of Cl atoms with cyclohexane, and their initial concentrations were determined from real-time profiles of HCl. The observed overall c-C(6)H(11) + c-C(6)H(11) rate constants demonstrate negative temperature dependence, which can be described by the following expressions: k(1) = 4.8 × 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1), with estimated uncertainty of 16% over the 303-520 K temperature range. The fraction of disproportionation equal to 41 ± 7% was determined at 305 K; analysis of earlier experimental determinations of the disproportionation-to-recombination branching ratio leads to recommending this room-temperature value for other temperatures. The corresponding temperature dependences of the recombination (1a, bicyclohexyl product) and the disproportionation (1b, cyclohexene and cyclohexane products) channels are k(1a) = 2.8 × 10(-12) exp(+542 K/T) and k(1b) = 2.0 × 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1), with estimated uncertainties of 20% and 29%, respectively.
环己基自由基的自反应动力学通过激光光解/光离子质谱法进行了研究。在 303-520 K 的温度区域和浴气（氦气中含有最多 5%的自由基前体）密度（3.00-12.0）×10(16)分子 cm(-3)下，通过草酸二氯((CClO)(2))的 193nm 光解与 Cl 原子与环己烷的快速反应相结合，直接实时实验中获得了总体速率常数，并通过 HCl 的实时分布来确定环己基自由基的初始浓度。观察到的整体 c-C(6)H(11) + c-C(6)H(11) 速率常数表现出负温度依赖性，可由以下表达式描述：k(1) = 4.8 × 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1)，在 303-520 K 的温度范围内，估计不确定度为 16%。在 305 K 时，确定歧化反应的分数等于 41 ± 7%；对歧化-复合分支比的早期实验测定的分析导致建议将此室温值用于其他温度。复合（1a，双环己基产物）和歧化（1b，环己烯和环己烷产物）通道的相应温度依赖性为 k(1a) = 2.8 × 10(-12) exp(+542 K/T) 和 k(1b) = 2.0 × 10(-12) exp(+542 K/T) cm(3) molecule(-1) s(-1)，估计不确定度分别为 20%和 29%。
