Biasin Elisa, van Driel Tim B, Levi Gianluca, Laursen Mads G, Dohn Asmus O, Moltke Asbjørn, Vester Peter, Hansen Frederik B K, Kjaer Kasper S, Harlang Tobias, Hartsock Robert, Christensen Morten, Gaffney Kelly J, Henriksen Niels E, Møller Klaus B, Haldrup Kristoffer, Nielsen Martin M
Department of Physics, Technical University of Denmark, Fysikvej 307, DK-2800 Kongens Lyngby, Denmark.
Department of Chemistry, Technical University of Denmark, Kemitorvet 207, DK-2800 Kongens Lyngby, Denmark.
J Synchrotron Radiat. 2018 Mar 1;25(Pt 2):306-315. doi: 10.1107/S1600577517016964. Epub 2018 Feb 13.
Time-resolved X-ray scattering patterns from photoexcited molecules in solution are in many cases anisotropic at the ultrafast time scales accessible at X-ray free-electron lasers (XFELs). This anisotropy arises from the interaction of a linearly polarized UV-Vis pump laser pulse with the sample, which induces anisotropic structural changes that can be captured by femtosecond X-ray pulses. In this work, a method for quantitative analysis of the anisotropic scattering signal arising from an ensemble of molecules is described, and it is demonstrated how its use can enhance the structural sensitivity of the time-resolved X-ray scattering experiment. This method is applied on time-resolved X-ray scattering patterns measured upon photoexcitation of a solvated di-platinum complex at an XFEL, and the key parameters involved are explored. It is shown that a combined analysis of the anisotropic and isotropic difference scattering signals in this experiment allows a more precise determination of the main photoinduced structural change in the solute, i.e. the change in Pt-Pt bond length, and yields more information on the excitation channels than the analysis of the isotropic scattering only. Finally, it is discussed how the anisotropic transient response of the solvent can enable the determination of key experimental parameters such as the instrument response function.
在溶液中光激发分子的时间分辨X射线散射图案，在许多情况下，在X射线自由电子激光（XFEL）可达到的超快时间尺度上是各向异性的。这种各向异性源于线性偏振紫外-可见泵浦激光脉冲与样品的相互作用，它会引起各向异性结构变化，而这种变化可以被飞秒X射线脉冲捕捉到。在这项工作中，描述了一种对分子集合产生的各向异性散射信号进行定量分析的方法，并展示了该方法的使用如何提高时间分辨X射线散射实验的结构灵敏度。该方法应用于在XFEL上对溶剂化二铂配合物进行光激发时测量的时间分辨X射线散射图案，并对其中涉及的关键参数进行了探索。结果表明，在该实验中对各向异性和各向同性差分散射信号进行联合分析，可以更精确地确定溶质中主要的光致结构变化，即Pt-Pt键长的变化，并且比仅分析各向同性散射能获得更多关于激发通道的信息。最后，讨论了溶剂的各向异性瞬态响应如何能够确定诸如仪器响应函数等关键实验参数。
