Recent studies have found an unusual way of dissociation in formaldehyde. It can be characterized by a hydrogen atom that separates from the molecule, but instead of dissociating immediately it roams around the molecule for a considerable amount of time and extracts another hydrogen atom from the molecule prior to dissociation. This phenomenon has been coined roaming and has since been reported in the dissociation of a number of other molecules. In this paper we investigate roaming in Chesnavich’s $$\hbox {CH}_4^+$$CH4+ model. During dissociation the free hydrogen must pass through three phase space bottleneck for the classical motion, that can be shown to exist due to unstable periodic orbits. None of these orbits is associated with saddle points of the potential energy surface and hence related to transition states in the usual sense. We explain how the intricate phase space geometry influences the shape and intersections of invariant manifolds that form separatrices, and establish the impact of these phase space structures on residence times and rotation numbers. Ultimately we use this knowledge to attribute the roaming phenomenon to particular heteroclinic intersections.

中文翻译：

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漫游反应动力学的相空间几何

最近的研究发现了一种不寻常的甲醛解离方式。它的特点是一个氢原子与分子分离，但不是立即解离，而是在分子周围游荡相当长的时间，并在解离之前从分子中提取另一个氢原子。这种现象被称为漫游，此后在许多其他分子的解离中得到了报道。在本文中，我们研究了 Chesnavich 的 $$\hbox {CH}_4^+$$CH4+ 模型中的漫游。在解离过程中，自由氢必须通过经典运动的三相空间瓶颈，这可以表明由于不稳定的周期性轨道而存在。这些轨道都与势能面的鞍点无关，因此与通常意义上的过渡态有关。我们解释了复杂的相空间几何形状如何影响形成分离的不变流形的形状和交集，并确定这些相空间结构对停留时间和旋转数的影响。最终，我们使用这些知识将漫游现象归因于特定的异宿交叉点。