Chemical Sciences and Engineering Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, Illinois 60439, United States.
J Phys Chem A. 2013 Jun 13;117(23):4750-61. doi: 10.1021/jp402484v. Epub 2013 Jun 4.
The recombination of allyl radicals (C3H5), generated from the dissociation of 1,5-hexadiene or allyl iodide dilute in krypton, has been investigated in a diaphragmless shock tube using laser schlieren densitometry, LS, (900-1700 K, 10 ± 1, 29 ± 3, 57 ± 3, and 120 ± 4 Torr). The LS density gradient profiles were simulated and excellent agreement was found between simulations and experimental profiles. Rate coefficients for C3H5I → C3H5 + I and C3H5 + C3H5 → C6H10 were obtained and showed strong fall-off. Second order rate coefficients for allyl radical recombination were determined as k(1a,124Torr) = (2.6 ± 0.8) × 10(55)T( -12.995) exp(-8426/T), k(1a,57Torr) = (1.7 ± 0.5) × 10(60)T( -14.49) exp(-9344/T), and k(1a,30Torr) = (7.5 ± 2.3) × 10(66)T( -15.935) exp(-10192/T) cm(3) mol(-1)s(-1). The contribution of a disproportionation channel in allyl radical reactions was assessed, and the best agreement was obtained with no more than 5% disproportionation. Notably, because both the forward and back reactions of C6H10 ⇌ C3H5 + C3H5 were measured, utilizing two different precursors, the equilibrium constant of this reaction could be found, suggesting an entropy of formation of 1,5-hexadiene, 87.3 cal mol(-1 )K(-1), which is significantly smaller than that group additivity predicts, but larger than other reference literature values.
丙烯基自由基（C3H5）的重组，是由 1,5-己二烯或丙烯基碘在氪中的离解产生的，已经在无膜激波管中使用激光纹影密度法（LS）进行了研究，（900-1700 K，10 ± 1，29 ± 3，57 ± 3 和 120 ± 4 Torr）。LS 密度梯度轮廓得到了模拟，模拟结果与实验轮廓非常吻合。得到了 C3H5I → C3H5 + I 和 C3H5 + C3H5 → C6H10 的速率系数，并显示出强烈的下降。确定了丙烯基自由基重组的二级速率系数，为 k(1a,124Torr) = (2.6 ± 0.8) × 10(55)T( -12.995) exp(-8426/T)，k(1a,57Torr) = (1.7 ± 0.5) × 10(60)T( -14.49) exp(-9344/T)，和 k(1a,30Torr) = (7.5 ± 2.3) × 10(66)T( -15.935) exp(-10192/T) cm(3) mol(-1)s(-1)。评估了丙烯基自由基反应中歧化通道的贡献，并且用不超过 5%的歧化反应获得了最佳吻合。值得注意的是，由于 C6H10 ⇌ C3H5 + C3H5 的正向和反向反应都被测量了，利用了两种不同的前体，可以找到这个反应的平衡常数，这表明 1,5-己二烯的生成焓为 87.3 cal mol(-1) K(-1)，这明显小于基团加和预测的值，但大于其他参考文献的值。
