Department of Chemistry, Institute of Science , Banaras Hindu University , Varanasi , 221005 , India.
J Phys Chem A. 2018 Apr 12;122(14):3556-3562. doi: 10.1021/acs.jpca.8b01386. Epub 2018 Apr 2.
The direct dynamics trajectory surface hopping (DDTSH) method has been employed to study the reaction of C(P) with ethylene (CH). Our trajectory simulations show that at a reagent collision energy of 7.36 kcal/mol, there are two possible product channels: propargyl (HCCCH) + H and carbene (CH) + acetylene (HCCH). Estimated branching ratios based on trajectory propagations indicate that propargyl radical formation is the dominant channel contributing (94.1 ± 5.2) % of the overall products formation with (5.9 ± 1.7)% contribution from the minor CH + HCCH channel. These findings are consistent with earlier experimental observations and theoretical predictions that propargyl (HCCCH) formation is the dominant channel for the C(P) + CH collision reaction. Our trajectory simulations, however, unravel five distinctly different dynamical pathways, unlike earlier experimental and theoretical predictions of only two pathways proposed for the formation of propargyl radical, and three different dynamics are followed for the CH + HCCH channel (this channel was not detected experimentally). The computed translational energy distribution for the propargyl + H channel is narrower and showed peak maximum at a lower energy compared to the experimental one. While the center of mass product angular distribution based on our trajectory propagation is nearly isotropic in nature indicating formation of long-lived intermediate complexes, the experimental one was reported to be backward-forward distributed with more intensity in the forward direction indicating the formation of an osculating complex. Our trajectory surface hopping calculations confirm that the effect of intersystem crossing (ISC) is not important for the title reaction presumably because of weak spin-orbit coupling values (<10 cm) for the (C + CH) system. No trace of cyclic products formation was obtained from our trajectory simulations, which however was predicted to be a minor (2%) product channel, experimentally.
已采用直接动力学轨迹表面跳跃（DDTSH）方法研究 C（P）与乙烯（CH）的反应。我们的轨迹模拟表明，在试剂碰撞能为 7.36 kcal/mol 时，存在两个可能的产物通道：丙炔基（HCCCH）+H 和卡宾（CH）+乙炔（HCCH）。基于轨迹传播的估算分支比表明，炔丙基自由基的形成是主要通道，占总产物形成的（94.1±5.2）%，而较小的 CH+HCCH 通道的贡献为（5.9±1.7）%。这些发现与早期的实验观察和理论预测一致，即丙炔基（HCCCH）的形成是 C（P）+CH 碰撞反应的主要通道。然而，与早期实验和理论预测提出的形成丙炔基自由基的两条途径不同，我们的轨迹模拟揭示了五条截然不同的动力学途径，并且对于 CH+HCCH 通道，也遵循了三种不同的动力学（该通道在实验中未被检测到）。与实验相比，用于丙炔基+H 通道的计算得到的平动能分布更窄，并且在较低的能量下显示出峰值最大值。虽然基于我们的轨迹传播的质心产物角分布在本质上几乎各向同性，表明形成长寿命的中间复合物，但实验报告的角分布是向后向前分布的，在向前方向上的强度更大，表明形成了一个盘旋复合物。我们的轨迹表面跳跃计算证实，对于标题反应，系间窜越（ISC）的影响不重要，大概是因为（C+CH）体系的自旋轨道耦合值较弱（<10 cm）。我们的轨迹模拟没有得到环状产物形成的痕迹，然而，实验预测这是一个次要（2%）的产物通道。
