Br $_2^+$中振动量子叠加态的阿秒XUV探测
Attosecond XUV probing of vibronic quantum superpositions in Br$_2^+$
摘要：
超快激光激发可以在分子中产生电子态的相干叠加，并在几到亚飞秒的时间尺度上触发电子密度的超快流动。虽然最近的阿秒实验已经解决了这些初级光化学过程的实时观测，同时核运动的基本作用以及它们如何修改和干扰价电子运动仍然不确定。在这里，我们调查的相干电子振动动力学诱导离子溴（Br $_2^+$），包括自旋轨道和价电子叠加，使用阿秒瞬态吸收光谱的多个振动能级之间。通过对Br- $3d$芯能级吸收信号的特征量子拍频测量电子相干的衰减、恢复和明显频移。量子力学模拟将观察到的电子退相干归因于非谐势上核波包的相位分布变宽。进一步揭示了分子电子振动结构是作为电子拍频的离散级数而被印记的。这些结果为解释多原子体系中复杂的电荷迁移动力学提供了基础。
英文摘要：
Ultrafast laser excitation can create coherent superpositions of electronic states in molecules and trigger ultrafast flow of electron density on few- to sub-femtosecond time scales. While recent attosecond experiments have addressed real-time observation of these primary photochemical processes, the underlying roles of simultaneous nuclear motions and how they modify and disturb the valence electronic motion remain uncertain. Here, we investigate coherent electronic-vibrational dynamics induced among multiple vibronic levels of ionic bromine (Br$_2^+$), including both spin-orbit and valence electronic superpositions, using attosecond transient absorption spectroscopy. Decay, revival, and apparent frequency shifts of electronic coherences are measured via characteristic quantum beats on the Br-$3d$ core-level absorption signals. Quantum-mechanical simulations attribute the observed electronic decoherence to broadened phase distributions of nuclear wave packets on anharmonic potentials. Molecular vibronic structure is further revealed to be imprinted as discrete progressions in electronic beat frequencies. These results provide a future basis to interpret complex charge-migration dynamics in polyatomic systems.
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