Haase Dietrich, Manz Jörn, Tremblay Jean Christophe
Institut für Chemie und Biochemie, Freie Universität Berlin, 14195 Berlin, Germany.
State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China.
J Phys Chem A. 2020 Apr 30;124(17):3329-3334. doi: 10.1021/acs.jpca.0c00404. Epub 2020 Apr 20.
Charge migration moves electrons from one molecular site to another, in a typical time domain from few hundred attoseconds to few femtoseconds. On this timescale, the nuclei stand practically still, implying that the nuclear point group symmetry is conserved. Because electrons move ultrafast, this can lead to a surprising effect, namely, breaking the spatial symmetry of the electron density in spite of the conservation of nuclear framework symmetry. We demonstrate theoretically that attosecond charge migration achieves this electron symmetry breaking if the electrons are prepared in a coherent superposition of nondegenerate electronic ground and excited states which transform according to different irreducible representations. Two simple examples provide a proof-of-principle, namely, periodic attosecond charge migration in the σ + σ superposition state of the aligned H cation (nuclear point group , but electron symmetry breaking → ) and in the A + B superposition state of the oriented HO molecule ( vs → ).
电荷迁移将电子从一个分子位点移动到另一个分子位点，典型的时域从几百阿秒到几飞秒。在此时间尺度上，原子核实际上静止不动，这意味着核点群对称性得以保留。由于电子移动极快，这可能导致一个惊人的效应，即尽管核框架对称性得以保留，但电子密度的空间对称性却被打破。我们从理论上证明，如果电子被制备在非简并电子基态和激发态的相干叠加态中，且这些态根据不同的不可约表示进行变换，那么阿秒电荷迁移就能实现这种电子对称性的打破。两个简单的例子提供了原理证明，即对齐的H阳离子（核点群 ，但电子对称性打破 → ）的σ + σ叠加态中的周期性阿秒电荷迁移，以及取向的HO分子（ 与 → ）的A + B叠加态中的周期性阿秒电荷迁移。
