Gannon Kelly L, Glowacki David R, Blitz Mark A, Hughes Kevin J, Pilling Michael J, Seakins Paul W
School of Chemistry, University of Leeds, Woodhouse Lane, Leeds, LS2 9JT, United Kingdom.
J Phys Chem A. 2007 Jul 26;111(29):6679-92. doi: 10.1021/jp0689520. Epub 2007 May 31.
The kinetics and H atom channel yield at both 298 and 195 K have been determined for reactions of CN radicals with C2H2 (1.00+/-0.21, 0.97+/-0.20), C2H4 (0.96+/-0.032, 1.04+/-0.042), C3H6 (pressure dependent), iso-C4H8 (pressure dependent), and trans-2-C4H8 (0.039+/-0.019, 0.029+/-0.047) where the first figure in each bracket is the H atom yield at 298 K and the second is that at 195 K. The kinetics of all reactions were studied by monitoring both CN decay and H atom growth by laser-induced fluorescence at 357.7 and 121.6 nm, respectively. The results are in good agreement with previous studies where available. The rate coefficients for the reaction of CN with trans-2-butene and iso-butene have been measured at 298 and 195 K for the first time, and the rate coefficients are as follows: k298K=(2.93+/-0.23)x10(-10) cm3 molecule(-1) s(-1), k195K=(3.58+/-0.43)x10(-10) cm3 molecule(-1) s(-1) and k298K=(3.17+/-0.10)x10(-10) cm3 molecule(-1) s(-1), k195K=(4.32+/-0.35)x10(-10) cm3 molecule(-1) s(-1), respectively, where the errors represent a combination of statistical uncertainty (2sigma) and an estimate of possible systematic errors. A potential energy surface for the CN+C3H6 reaction has been constructed using G3X//UB3LYP electronic structure calculations identifying a number of reaction channels leading to either H, CH3, or HCN elimination following the formation of initial addition complexes. Results from the potential energy surface calculations have been used to run master equation calculations with the ratio of primary:secondary addition, the average amount of downward energy transferred in a collision DeltaEd, and the difference in barrier heights between H atom elimination and an H atom 1, 2 migration as variable parameters. Excellent agreement is obtained with the experimental 298 K H atom yields with the following parameter values: secondary addition complex formation equal to 80%, DeltaEd=145 cm(-1), and the barrier height for H atom elimination set 5 kJ mol(-1) lower than the barrier for migration. Finally, very low temperature master equation simulations using the best fit parameters have been carried out in an increased precision environment utilizing quad-double and double-double arithmetic to predict H and CH3 yields for the CN+C3H6 reaction at temperatures and pressures relevant to Titan. The H and CH3 yields predicted by the master equation have been parametrized in a simple equation for use in modeling.
已测定了在298 K和195 K下，CN自由基与C2H2（1.00±0.21，0.97±0.20）、C2H4（0.96±0.032，1.04±0.042）、C3H6（与压力有关）、异丁烯（与压力有关）和反式-2-丁烯（0.039±0.019，0.029±0.047）反应的动力学和H原子通道产率，其中每个括号中的第一个数字是298 K时的H原子产率，第二个数字是195 K时的H原子产率。通过分别在357.7 nm和121.6 nm处用激光诱导荧光监测CN的衰减和H原子的生成，研究了所有反应的动力学。在有可用数据的情况下，结果与先前的研究结果吻合良好。首次在298 K和195 K下测量了CN与反式-2-丁烯和异丁烯反应的速率系数，速率系数如下：k298K =(2.93±0.23)×10(-10) cm3·分子(-1)·s(-1)，k195K =(3.58±0.43)×10(-10) cm3·分子(-1)·s(-1)；以及k298K =(3.17±0.10)×10(-10) cm3·分子(-1)·s(-1)，k195K =(4.32±0.35)×10(-10) cm3·分子(-1)·s(-1)，其中误差表示统计不确定性（2σ）和可能的系统误差估计值的组合。使用G3X//UB3LYP电子结构计算构建了CN + C3H6反应的势能面，确定了一些反应通道，这些通道在形成初始加成复合物后导致H、CH3或HCN消除。势能面计算结果已用于进行主方程计算，将初级加成与次级加成的比例、碰撞中向下转移的平均能量ΔEd以及H原子消除与H原子1, 2迁移之间的势垒高度差作为可变参数。通过以下参数值，实验得到的298 K H原子产率与计算结果取得了极好的吻合：次级加成复合物形成率等于80%，ΔEd = 145 cm(-1)，H原子消除的势垒高度设定为比迁移势垒低5 kJ·mol(-1)。最后，在利用四倍双精度和双精度双精度算法的高精度环境中，使用最佳拟合参数进行了极低温主方程模拟，以预测与土卫六相关的温度和压力下CN + C3H6反应的H和CH3产率。主方程预测的H和CH3产率已被参数化到一个简单方程中，用于建模。
