AI 中文总结
本研究结合完全活性空间二阶微扰理论的表面跳跃动力学与MR-ADC，模拟AcAc瞬态X射线吸收光谱，揭示其响应机制，为AcAc光弛豫提供完整机制图景。
AI 中文摘要
时间分辨X射线吸收光谱（TR-XAS）可提供耦合电子与核动力学的元素及位点特异性探针，但其解读需能处理非平衡核系综下多组态激发态的方法。本研究通过结合完全活性空间二阶微扰理论的表面跳跃动力学与多参考代数图论构造（MR-ADC），报道乙酰丙酮（AcAc）瞬态X射线吸收光谱的时间分辨模拟。模拟得到的20-200 fs光谱与实验测量结果吻合良好，揭示TR-XAS响应由单重态势能面（S2和S1）上连续演化的分子几何分布主导。具体而言，279.5-281.5 eV处的吸收因瞬态近对称质子共享构型而增强，而284-286 eV的谱线反映了受质子转移、键交替及开环调控的几何依赖性C1s激发。对于长时间T1光谱（7-10 ps），281.4和283.8 eV附近的主要特征被归为中心C 1s向低能三重态π轨道的激发。综上，本研究的模拟通过将超快碳K边信号与质子转移、骨架重组、内转换及三重态形成直接关联，为AcAc光弛豫提供了更完整的机制图景。
英文摘要
Time-resolved X-ray absorption spectroscopy (TR-XAS) offers an element- and site-specific probe of coupled electronic and nuclear dynamics, but its interpretation requires methods that can treat multiconfigurational excited states across nonequilibrium nuclear ensembles. Here, we report time-resolved simulations of the acetylacetone (AcAc) transient X-ray absorption spectra by combining surface-hopping dynamics from complete active space second-order perturbation theory with multireference algebraic diagrammatic construction (MR-ADC). The simulated 20-200 fs spectra show a good agreement with experimental measurements and reveal that the TR-XAS response is governed by continuously evolving distributions of molecular geometries on the singlet potential energy surfaces (S2 and S1). In particular, absorption at 279.5-281.5 eV is enhanced for transient, nearly symmetric proton-sharing configurations, whereas the 284-286 eV profile reflects geometry-dependent C1s excitations modulated by proton transfer, bond alternation, and ring opening. For the long-time T_1 spectrum (7-10 ps), the principal features near 281.4 and 283.8 eV are assigned to central C 1s excitations into low-lying triplet pi-orbitals. Together, our simulations provide a more complete mechanistic picture of AcAc photorelaxation by directly linking ultrafast carbon K-edge signals to proton transfer, skeletal reorganization, internal conversion, and triplet formation.
