Ruberti M
Department of Physics, Imperial College London, Prince Consort Road, London SW7 2AZ, UK.
Faraday Discuss. 2021 May 27;228(0):286-311. doi: 10.1039/d0fd00104j.
Here I present a fully ab initio time-resolved study of X-ray attosecond transient absorption spectroscopy (ATAS) in a prototypical polyatomic molecule, pyrazine, and demonstrate the possibility of retrieving the many-electron quantum ionic coherences arising in attosecond molecular photoionisation and pre-determining the subsequent charge-directed photochemical reactivity. Advanced first-principles many-electron simulations are performed, within a hybrid XUV pump/X-ray probe setup, to describe the interaction of pyrazine with both XUV pump and X-ray probe pulses, and study the triggered correlated many-electron dynamics. The calculations are carried out by means of the recently-developed ab initio method for many-electron dynamics in polyatomic molecules, the time-dependent (TD) B-spline Restricted Correlation Space-Algebraic Diagrammatic Construction (RCS-ADC). RCS-ADC simulates molecular ionisation from first principles, combining the accurate description of electron correlation of quantum chemistry with the full account of the continuum dynamics of the photoelectron. Complete theoretical characterisation of the atto-ionised many-electron state and photo-induced attosecond charge dynamics is achieved by calculating the reduced ionic density matrix (R-IDM) of the bipartite ion-photoelectron system, with full inclusion of the correlated shakeup states. Deviations from the sudden approximation picture of photoionisation, in the low-photon-energy limit, are presented. The effect of the multi-channel interaction between the parent-ion and the emitted photoelectron on the onset of the quantum electronic coherences is analysed. Moreover, I show how the Schmidt decomposition of the R-IDM unravels the many-electron dynamics triggered by the pump, allowing for the identification of the key channels involved. Finally, I calculate the X-ray attosecond transient absorption spectra of XUV-ionised pyrazine. The results unveil the mapping of the ATAS measurement onto the quantum electronic coherences, and related non-zero R-IDM matrix elements, produced upon ionisation by the XUV pump laser pulse.
在此，我展示了对典型多原子分子吡嗪进行的全从头算时间分辨X射线阿秒瞬态吸收光谱（ATAS）研究，并证明了获取阿秒分子光电离过程中产生的多电子量子离子相干性以及预先确定后续电荷导向光化学反应性的可能性。在混合极紫外（XUV）泵浦/X射线探测装置中进行了先进的第一性原理多电子模拟，以描述吡嗪与XUV泵浦脉冲和X射线探测脉冲的相互作用，并研究触发的相关多电子动力学。计算是通过最近开发的用于多原子分子多电子动力学的从头算方法——含时（TD）B样条受限相关空间代数图示构建（RCS - ADC）进行的。RCS - ADC从第一原理模拟分子电离，将量子化学中电子相关性的精确描述与光电子连续体动力学的全面考虑相结合。通过计算二分离子 - 光电子系统的约化离子密度矩阵（R - IDM），并充分考虑相关的振激态，实现了对阿秒电离多电子态和光诱导阿秒电荷动力学的完整理论表征。展示了在低光子能量极限下与光电离的突然近似图景的偏差。分析了母离子与发射光电子之间的多通道相互作用对量子电子相干性起始的影响。此外，我展示了R - IDM的施密特分解如何揭示由泵浦触发的多电子动力学，从而能够识别涉及的关键通道。最后，我计算了XUV电离的吡嗪的X射线阿秒瞬态吸收光谱。结果揭示了ATAS测量与量子电子相干性以及由XUV泵浦激光脉冲电离产生的相关非零R - IDM矩阵元之间的映射关系。
