Motion picture of a conical intersection In most chemical reactions, electrons move earlier and faster than nuclei. It is therefore common to model reactions by using potential energy surfaces that depict nuclear motion in a particular electronic state. However, in certain cases, two such surfaces connect in a conical intersection that mingles ultrafast electronic and nuclear rearrangements. Yang et al. used electron diffraction to obtain time-resolved images of CF3I molecules traversing a conical intersection in the course of photolytic cleavage of the C–I bond (see the Perspective by Fielding). Science, this issue p. 64; see also p. 30 Electron diffraction reveals the interplay of electronic and nuclear motion during light-induced scission of a C–I bond. Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.

中文翻译：

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用超快电子衍射成像 CF3I 锥形交叉和光解动力学

锥形交叉点的电影 在大多数化学反应中，电子比原子核移动得更早更快。因此，通常通过使用描述特定电子状态下的核运动的势能面来模拟反应。然而，在某些情况下，两个这样的表面连接成一个锥形交叉点，混合了超快的电子和核重排。杨等人。使用电子衍射获得 CF3I 分子在 C-I 键光解过程中穿过锥形交叉点的时间分辨图像（参见 Fielding 的观点）。科学，这个问题 p。64; 另见第。30 电子衍射揭示了光诱导 C-I 键断裂过程中电子和核运动的相互作用。锥形交叉点在多原子分子的激发态动力学中起着关键作用，因为它们控制着许多非绝热过程的反应途径。然而，超快探测器缺乏足够的空间分辨率来直接对通过这些交叉点的​​波包轨迹进行成像。在这里，我们展示了使用超快气相电子衍射对孤立的 CF3I 分子中的单光子和双光子激发通道的同时实验表征。在双光子通道中，我们绘制了相干核波包的实空间轨迹，当通过锥形交叉点时，它会分叉到两个势能面上。在单光子通道中，我们已经解决了多核维度中 CF3 碎片中伞形和呼吸振动模式的激发。这些发现对 ab initio 非绝热动力学计算进行了基准测试和验证。