Anisotropy enhanced X-ray scattering from solvated transition metal complexes

TL;DR

This paper introduces a method to analyze anisotropic X-ray scattering signals from photoexcited molecules in solution, enhancing the structural sensitivity and providing more detailed insights into ultrafast molecular changes at XFELs.

Contribution

The work presents a quantitative analysis technique for anisotropic scattering signals, demonstrating its application to improve structural determination in time-resolved X-ray experiments.

Findings

Enhanced accuracy in measuring Pt-Pt bond length changes.

More detailed information on excitation channels.

Potential to determine experimental parameters like Instrument Response Function.

Abstract

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 we describe a method for quantitative analysis of the anisotropic scattering signal arising from an ensemble of molecules and we demonstrate how its use can enhance the structural sensitivity of the time-resolved X-ray scattering experiment. We apply this method on time-resolved X-ray scattering patterns measured upon photoexcitation of a solvated di-platinum complex at an XFEL and explore the key parameters involved. We show 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, we discuss how the anisotropic transient response of the solvent can enable the determination of key experimental parameters such as the Instrument Response Function.