Department of Chemistry and Cherry L. Emerson Center for Scientific Computation, Emory University, Atlanta, Georgia 30322, USA.
J Chem Phys. 2012 Dec 14;137(22):22A532. doi: 10.1063/1.4746758.
The reaction of O((3)P) with C(2)H(4), of importance in combustion and atmospheric chemistry, stands out as paradigm reaction involving not only the indicated triplet state potential energy surface (PES) but also an interleaved singlet PES that is coupled to the triplet surface. This reaction poses great challenges for theory and experiment, owing to the ruggedness and high dimensionality of these potentials, as well as the long lifetimes of the collision complexes. Crossed molecular beam (CMB) scattering experiments with soft electron ionization detection are used to disentangle the dynamics of this polyatomic multichannel reaction at a collision energy E(c) of 8.4 kcal∕mol. Five different primary products have been identified and characterized, which correspond to the five exothermic competing channels leading to H + CH(2)CHO, H + CH(3)CO, CH(3) + HCO, CH(2) + H(2)CO, and H(2) + CH(2)CO. These experiments extend our previous CMB work at higher collision energy (E(c) ∼ 13 kcal∕mol) and when the results are combined with the literature branching ratios from kinetics experiments at room temperature (E(c) ∼ 1 kcal∕mol), permit to explore the variation of the branching ratios over a wide range of collision energies. In a synergistic fashion, full-dimensional, QCT surface hopping calculations of the O((3)P) + C(2)H(4) reaction using ab initio PESs for the singlet and triplet states and their coupling, are reported at collision energies corresponding to the CMB and the kinetics ones. Both theory and experiment find almost an equal contribution from the triplet and singlet surfaces to the reaction, as seen from the collision energy dependence of branching ratios of product channels and extent of intersystem crossing (ISC). Further detailed comparisons at the level of angular distributions and translational energy distributions are made between theory and experiment for the three primary radical channel products, H + CH(2)CHO, CH(3) + HCO, and CH(2) + H(2)CO. The very good agreement between theory and experiment indicates that QCT surface-hopping calculations, using reliable coupled multidimensional PESs, can yield accurate dynamical information for polyatomic multichannel reactions in which ISC plays an important role.
O((3)P)与 C(2)H(4)的反应在燃烧和大气化学中具有重要意义，它是一个典范反应，不仅涉及到 indicated triplet state potential energy surface (PES)，还涉及到交错的 singlet PES，该 PES 与 triplet surface 耦合。由于这些势能的崎岖和高维性以及碰撞复合物的长寿命，该反应对理论和实验都构成了巨大的挑战。Crossed molecular beam (CMB)散射实验与软电子电离检测相结合，用于在碰撞能 E(c)为 8.4 kcal∕mol 时分离这个多原子多通道反应的动力学。已经鉴定和表征了五种不同的主要产物，它们对应于五个放热的竞争通道，分别通向 H + CH(2)CHO、H + CH(3)CO、CH(3) + HCO、CH(2) + H(2)CO 和 H(2) + CH(2)CO。这些实验扩展了我们之前在更高碰撞能（E(c)∼13 kcal∕mol）下的 CMB 工作，并且当将这些结果与室温下动力学实验的文献分支比（E(c)∼1 kcal∕mol）相结合时，可以探索分支比在很宽的碰撞能范围内的变化。以协同的方式，使用 singlet 和 triplet 状态的从头算 PES 及其耦合，报告了全维、QCT 表面跳跃计算 O((3)P) + C(2)H(4)反应在与 CMB 和动力学相对应的碰撞能下的反应。从产物通道分支比和体系间窜跃（ISC）的程度对碰撞能的依赖性来看，理论和实验都发现来自 triplet 和 singlet 表面的反应贡献几乎相等。对于三个主要的自由基通道产物 H + CH(2)CHO、CH(3) + HCO 和 CH(2) + H(2)CO，在理论和实验之间进行了角度分布和平移能分布的更详细比较。理论和实验之间非常好的一致性表明，使用可靠的耦合多维 PES 的 QCT 表面跳跃计算可以为多原子多通道反应提供准确的动力学信息，其中 ISC 起着重要作用。
