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 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 - UED) and spectroscopic (Time-Resolved PhotoElectron Spectroscopy - TRPES) measurements to follow the coupled electronic and nuclear dynamics involved in the internal conversion and photodissociation of the polyatomic molecule, diiodomethane (CH${}_2$I${}_2$). While UED directly probes the 3D nuclear dynamics, TRPES only serves as an indirect probe of nuclear dynamics via Franck-Condon factors, but 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 non-local dynamics captured by different groups of trajectories in the calculations.~This is the first time that both UED and TRPES are combined with theory capable of calculating the observables in both cases, yielding a direct view of the structural and non-adiabatic dynamics involved.

中文翻译：

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时间分辨光电子能谱和超快电子衍射的激发态分子动力学的光谱和结构探测

泵浦探针测量的目的是在发生化学和物理转换时捕获电子和原子核在其自然时标（飞秒到阿秒）上的运动，有效地利用短光脉冲进行。〜但是，感兴趣的量子动力学被坐标过滤了依赖于所选实验观察矩阵的元素。〜因此，只有通过实验测量和理论计算的组合，才能洞悉内部动力学。〜这里我们报告了结构（相对论超快电子衍射- UED）和分光光度法（时间分辨光电子能谱-TRPES）测量，以跟踪参与多原子分子二碘甲烷（CH）的内部转化和光解离的耦合电子和核动力学${}_2$一世${}_2$）。UED直接探测3D核动力学，而TRPES仅通过Franck-Condon因子充当核动力学的间接探测，但对电子能量和构型敏感，通过Koopmans相关性和光电子角分布}。具有轨迹表面跳变计算功能，能够从相同的动力学计算中模拟两次测量的观测值。〜测量结果突出了计算中不同轨迹组捕获的非局部动力学。〜这是两个UED首次将TRPES和TRPES与能够在两种情况下计算可观测值的理论相结合，可以直接查看所涉及的结构和非绝热动力学。