Paul Scherrer Institute , Villigen, Switzerland.
Department of Physics, University of Fribourg , Fribourg, Switzerland.
Struct Dyn. 2014 Mar 17;1(2):021101. doi: 10.1063/1.4868260. eCollection 2014 Mar.
Physical, biological, and chemical transformations are initiated by changes in the electronic configuration of the species involved. These electronic changes occur on the timescales of attoseconds (10(-18) s) to femtoseconds (10(-15) s) and drive all subsequent electronic reorganization as the system moves to a new equilibrium or quasi-equilibrium state. The ability to detect the dynamics of these electronic changes is crucial for understanding the potential energy surfaces upon which chemical and biological reactions take place. Here, we report on the determination of the electronic structure of matter using a single self-seeded femtosecond x-ray pulse from the Linac Coherent Light Source hard x-ray free electron laser. By measuring the high energy resolution off-resonant spectrum (HEROS), we were able to obtain information about the electronic density of states with a single femtosecond x-ray pulse. We show that the unoccupied electronic states of the scattering atom may be determined on a shot-to-shot basis and that the measured spectral shape is independent of the large intensity fluctuations of the incoming x-ray beam. Moreover, we demonstrate the chemical sensitivity and single-shot capability and limitations of HEROS, which enables the technique to track the electronic structural dynamics in matter on femtosecond time scales, making it an ideal probe technique for time-resolved X-ray experiments.
物理、生物和化学转化是由参与物种的电子构型变化引发的。这些电子变化发生在阿秒（10^(-18)秒）到飞秒（10^(-15)秒）的时间尺度内，并在系统达到新的平衡或准平衡状态时驱动所有后续的电子重新排列。能够检测这些电子变化的动力学对于理解化学和生物反应发生的势能面至关重要。在这里，我们报告了使用来自 Linac Coherent Light Source 硬 X 射线自由电子激光的单个自种子飞秒 X 射线脉冲来确定物质的电子结构。通过测量高能量分辨率非共振光谱（HEROS），我们能够用单个飞秒 X 射线脉冲获得关于电子态密度的信息。我们表明，可以在单次拍摄的基础上确定散射原子的未占据电子态，并且测量的光谱形状与入射 X 射线束的大强度波动无关。此外，我们展示了 HEROS 的化学灵敏度和单次拍摄能力和局限性，这使得该技术能够在飞秒时间尺度上跟踪物质中的电子结构动力学，使其成为时间分辨 X 射线实验的理想探针技术。
