Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction
Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction
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DOI：
10.1103/physrevx.10.021016
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发表时间：
2020-04-22
影响因子：
12.5
通讯作者：
Weinacht, Thomas
中科院分区：
文献类型：
--
作者：
Liu, Yusong;Horton, Spencer L.;Weinacht, Thomas
泵浦-探测测量的目的是捕捉电子和原子核在其自然时间尺度（飞秒到阿秒）上的运动，因为化学和物理转换发生了，有效地用短光脉冲制作“分子电影”。然而，感兴趣的量子动力学被所选择的实验观测的坐标相关的矩阵元素过滤。因此，只有通过实验测量和理论计算相结合，才能深入了解内部动力学。在这里，我们报告的结构（相对论超快电子衍射，或UED）和光谱（时间分辨光电子能谱，或TRPES）测量相结合，遵循耦合的电子和核动力学参与的多原子分子，二碘甲烷（CH 2 I2）的内部转换和光解离。虽然UED直接探测3D核动力学，TRPES仅通过Franck-Condon因子作为核动力学的间接探测，但它通过Koopmans关联和光电子角分布对电子能量和构型敏感。这两个测量解释与轨迹表面跳跃计算，这是能够模拟从相同的动力学计算的两个测量的观测值。测量突出了计算中不同轨迹组捕获的非局部动态。这是第一次，UED和TRPES结合理论能够计算在这两种情况下的观测量，产生直接的结构和非绝热动力学。
Pump-probe measurements aim to capture the motion of electrons and nuclei on their natural timescales (femtoseconds to attoseconds) as chemical and physical transformations take place, effectively making "molecular movies" with short light pulses. However, the quantum dynamics of interest are filtered by the coordinate-dependent matrix elements of the chosen experimental observable. Thus, it is only through a combination of experimental measurements and theoretical calculations that one can gain insight into the internal dynamics. Here, we report on a combination of structural (relativistic ultrafast electron diffraction, or UED) and spectroscopic (time-resolved photoelectron spectroscopy, or TRPES) measurements to follow the coupled electronic and nuclear dynamics involved in the internal conversion and photodissociation of the polyatomic molecule, diiodomethane (CH2I2). While UED directly probes the 3D nuclear dynamics, TRPES only serves as an indirect probe of nuclear dynamics via Franck-Condon factors, but it is sensitive to electronic energies and configurations, via Koopmans' correlations and photoelectron angular distributions. These two measurements are interpreted with trajectory surface hopping calculations, which are capable of simulating the observables for both measurements from the same dynamics calculations. The measurements highlight the nonlocal dynamics captured by different groups of trajectories in the calculations. For the first time, both UED and TRPES are combined with theory capable of calculating the observables in both cases, yielding a direct view of the structural and nonadiabatic dynamics involved.