Toward Understanding the Roaming Mechanism in H + MgH → Mg + HH Reaction.

The roaming mechanism in the reaction H + MgH →Mg + HH is investigated by classical and quantum dynamics employing an accurate ab initio three-dimensional ground electronic state potential energy surface. The reaction dynamics are explored by running trajectories initialized on a four-dimensional dividing surface anchored on three-dimensional normally hyperbolic invariant manifold associated with a family of unstable orbiting periodic orbits in the entrance channel of the reaction (H + MgH). By locating periodic orbits localized in the HMgH well or involving H orbiting around the MgH diatom, and following their continuation with the total energy, regions in phase space where reactive or nonreactive trajectories may be trapped are found. In this way roaming reaction pathways are deduced in phase space. Patterns similar to periodic orbits projected into configuration space are found for the quantum bound and resonance eigenstates. Roaming is attributed to the capture of the trajectories in the neighborhood of certain periodic orbits. The complex forming trajectories in the HMgH well can either return to the radical channel or "roam" to the MgHH minimum from where the molecule may react.

利用精确的从头算三维基态电子态势能面，通过经典和量子动力学研究了反应H + MgH → Mg + HH中的漫游机制。通过在一个四维分界面上初始化轨迹来探索反应动力学，该分界面基于与反应（H + MgH）入口通道中一族不稳定的轨道周期轨道相关的三维正常双曲不变流形。通过定位局限在HMgH势阱内或涉及H围绕MgH双原子轨道运动的周期轨道，并随着总能量对其进行延续，找到了相空间中可能捕获反应性或非反应性轨迹的区域。通过这种方式在相空间中推导出了漫游反应路径。对于量子束缚态和共振本征态，发现了与投影到构型空间中的周期轨道相似的模式。漫游归因于轨迹在某些周期轨道附近的捕获。HMgH势阱中的复合物形成轨迹既可以返回自由基通道，也可以“漫游”到MgHH极小值处，分子可能从那里发生反应。