Stereodynamics of multistate roaming.
Stereodynamics of multistate roaming.
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DOI：
10.1039/c2cp40235a
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发表时间：
2012-04
期刊：
影响因子：
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通讯作者：
M. Grubb;M. Warter;S. North
中科院分区：
文献类型：
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作者：
M. Grubb;M. Warter;S. North
我们利用离子成像实验和最近的理论研究结果，对实验观察到的两种反应途径的 NO3 → NO + O2 光解进行了分子水平描述。为了进一步表征该反应的立体动力学，对状态选择的 NO 片段进行了矢量相关和 Λ 双峰倾向测量。先前对相对 Λ 双峰倾向的测量（Grubb 等人，Science，2012，1075-1078）以及从头算起的计算表明，这两条路径均源自漫游型机制，但每条路径均源自不同电子势的漫游。然而，该模型假设 NO3 解离发生在分子平面上。在本文中，我们通过速度相关矢量相关测量证实了这一假设。在源自两条路径的 NO 片段中观察到速度矢量 v 和角动量矢量 j 之间的强垂直相关性，这与受约束的平面解离一致。这些结果是根据其他漫游系统中不存在矢量相关性来讨论的，这些漫游系统以前的特点是不受约束的分子内抽象。我们表明，几何约束实际上在漫游动力学中应该相当普遍，并且类似于相应的双分子抽象反应的几何约束。
We present a molecular level description of NO3→ NO + O2 photodissociation for both of the experimentally observed reaction pathways using the results of ion imaging experiments and recent theoretical studies. Vector correlation and Λ doublet propensity measurements have been performed on state-selected NO fragments in order to further characterize the stereodynamics of this reaction. Previous measurements (Grubb et al., Science, 2012, 1075-1078) of relative Λ doublet propensities along with ab initio calculations revealed that both pathways arise from roaming-type mechanisms, but each pathway arises from roaming on a different electronic potential. This model, however, assumes that NO3 dissociation takes place in the molecular plane. In the present paper, we have confirmed this assumption through speed-dependent vector correlation measurements. Strong perpendicular correlations between the velocity vector v and the angular momentum vector j are observed in the NO fragment originating from both pathways, in agreement with a constrained planar dissociation. These results are discussed in light of the absence of vector correlations in other roaming systems, which have previously been characterized by an unconstrained intra-molecular abstraction. We show that geometrical constraints should in fact be quite prevalent in roaming dynamics, and are analogous to the geometrical constraints of the corresponding bimolecular abstraction reaction.