Balucani Nadia, Leonori Francesca, Casavecchia Piergiorgio, Fu Bina, Bowman Joel M
Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia , 06123 Perugia, Italy.
State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Sciences , Dalian 116023, China.
J Phys Chem A. 2015 Dec 17;119(50):12498-511. doi: 10.1021/acs.jpca.5b07979. Epub 2015 Oct 6.
The combustion relevant O((3)P) + C2H4 reaction stands out as a prototypical multichannel nonadiabatic reaction involving both triplet and singlet potential energy surfaces (PESs), which are strongly coupled. Crossed molecular beam (CMB) scattering experiments with universal soft electron ionization mass spectrometric detection have been used to characterize the dynamics of this reaction at the relatively high collision energy Ec of 13.7 kcal/mol, attained by crossing the reactant beams at an angle of 135°. This work is a full report of the data at the highest Ec investigated for this reaction. From laboratory product angular and velocity distribution measurements, angular and translational energy distributions in the center-of-mass system have been obtained for the five observed exothermic competing reaction channels leading to H + CH2CHO, H + CH3CO, CH3 + HCO, CH2 + H2CO, and H2 + CH2CO. The product branching ratios (BRs) have been derived. The elucidation of the reaction dynamics is assisted by synergic full-dimensional quasiclassical trajectory surface-hopping calculations of the reactive differential cross sections on coupled ab initio triplet/singlet PESs. This joint experimental/theoretical study extends and complements our previous combined CMB and theoretical work at the lower collision energy of 8.4 kcal/mol. The theoretically derived BRs and extent of intersystem crossing (ISC) are compared with experimental results. In particular, the predictions of the QCT results for the three main channels (those leading to vinoxy + H, methyl + HCO and methylene + H2CO formation) are compared directly with the experimental data in the laboratory frame. Good overall agreement is noted between theory and experiment, although some small, yet significant shortcomings of the theoretical differential cross section are noted. Both experiment and theory find almost an equal contribution from the triplet and singlet surfaces to the reaction, with a clear tendency of the degree of ISC to decrease with increasing Ec and with theory slightly overestimating the extent of ISC.
与燃烧相关的O((3)P) + C2H4反应是一个典型的多通道非绝热反应，涉及强烈耦合的三重态和单重态势能面（PESs）。利用具有通用软电子电离质谱检测的交叉分子束（CMB）散射实验，在相对较高的碰撞能量Ec = 13.7 kcal/mol下表征了该反应的动力学，通过以135°的角度交叉反应物束实现。这项工作是对该反应所研究的最高Ec下的数据的完整报告。通过实验室产物角分布和速度分布测量，获得了质心系统中导致H + CH2CHO、H + CH3CO、CH3 + HCO、CH2 + H2CO和H2 + CH2CO的五个观察到的放热竞争反应通道的角分布和平动能分布。推导了产物分支比（BRs）。通过对耦合的从头算三重态/单重态PESs上的反应性微分截面进行全维准经典轨迹表面跳跃计算，辅助阐明反应动力学。这项联合实验/理论研究扩展并补充了我们之前在8.4 kcal/mol较低碰撞能量下的CMB和理论相结合的工作。将理论推导的BRs和系间窜越（ISC）程度与实验结果进行了比较。特别是，将三个主要通道（导致生成乙烯氧基 + H、甲基 + HCO和亚甲基 + H2CO的通道）的量子经典轨迹（QCT）结果预测直接与实验室坐标系中的实验数据进行了比较。理论与实验之间总体上吻合良好，尽管注意到理论微分截面存在一些虽小但显著的不足。实验和理论都发现三重态和单重态表面对反应的贡献几乎相等，并且ISC程度有随Ec增加而降低的明显趋势，理论略微高估了ISC的程度。
