CF3CH3 → HF+CF2CH2:: A non-RRKM reaction?
CF3CH3 → HF+CF2CH2:: A non-RRKM reaction?
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DOI：
10.1021/jp054510x
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发表时间：
2006-03-09
影响因子：
2.9
通讯作者：
Leitner, DM
中科院分区：
文献类型：
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作者：
Barker, JR;Stimac, PJ;Leitner, DM
基弗等人[J. Phys. Chem. A 2004，108，2443-2450]最近报道的标题反应在1600和2400 K之间的实验激波管数据已经与使用三种模型的主方程模拟进行了比较：（a）标准RRKM理论，（B）通过局部随机矩阵理论修改的RRKM理论，其引入由缓慢的分子内振动能随机化引起的动力学校正，和（c）一个特别的经验非RRKM模型。只有第三个模型提供了基弗等人的单分子反应速率数据的良好拟合。在单独的模拟中，当能量传递参数自由变化以拟合数据时，所有三个模型都准确地再现了Marcoux和Setser [J. Phys. Chem. 1978，82，97-108]的实验300 K化学活化数据。当使用几何异构体（1，1，2-三氟乙烷）的实验能量传递参数时，标准RRKM模型比其他模型更好地拟合化学活化数据，但是如果与1，1，2异构体相比，1，1，1-三氟乙烷中的能量传递显著降低，则经验特设非RRKM模型也给出了良好的拟合。虽然特设的经验非RRKM模型可以拟合的数据，它不是基于理论，我们认为，这是物理上不现实的。我们还表明，主方程模拟可以模仿基弗等人的振动弛豫数据，这是第一个双指数弛豫的激波管观察。我们的结论是，在获得更多关于三氟乙烷的数据之前，目前的证据不足以确定非RRKM效应在该反应中是否重要，或者基弗等人的数据是否可以用其他方式解释。
The experimental shock tube data recently reported by Kiefer et al. [J. Phys. Chem. A 2004, 108, 2443-2450] for the title reaction at temperatures between 1600 and 2400 K have been compared to master equation simulations using three models: (a) standard RRKM theory, (b) RRKM theory modified by local random matrix theory, which introduces dynamical corrections arising from slow intramolecular vibrational energy randomization, and (c) an ad hoc empirical non-RRKM model. Only the third model provides a good fit of the Kiefer et al. unimolecular reaction rate data. In separate simulations, all three models accurately reproduce the experimental 300 K chemical activation data of Marcoux and Setser [J. Phys. Chem. 1978, 82, 97-108] when the energy transfer parameters are freely varied to fit the data. When experimental energy transfer parameters for a geometrical isomer (1,1,2-trifluoroethane) are used, the standard RRKM model fits the chemical activation data better than the other models, but if energy transfer in the 1,1,1-trifluoroethane is significantly reduced in comparison to the 1, 1,2 isomer, then the empirical ad hoc non-RRKM model also gives a good fit. While the ad hoc empirical non-RRKM model can be made to fit the data, it is not based on theory, and we argue that it is physically unrealistic. We also show that the master equation simulations can mimic the Kiefer et al. vibrational relaxation data, which was the first shock tube observation of double-exponential relaxation. We conclude that, until more data on the trifluoroethanes become available, the current evidence is insufficient to decide with confidence whether non-RRKM effects are important in this reaction, or whether the Kiefer et al. data can be explained in some other way.