Time-resolved structural dynamics with X-rays: A theoretical perspective of resolving ultrafast processes in the condensed phase Seminar

 

Visualising an evolving molecular structure during the course of a chemical reaction or biological function has been the ultimate goal of scientists for decades. Ultrafast studies that emerged with the implementation of femtosecond-picosecond linear and nonlinearoptical spectroscopies have had a huge impact on our understanding of chemical reactions, biological functions and phase transitions in materials owing to their ability to probe, in real-time, the nuclear motion within these different types of systems. However, for systems of more than two atoms the link between the optical domain spectroscopic observables and the molecular structure is ambiguous and therefore from the early days of ultrafast spectroscopy much effort was invested to develop methods that achieve both high temporal (on the femtosecond time scale) and spatial (on the order on tenths of an angstr¨om) resolution [1].

For this, time-resolved X-ray spectroscopies are ideal due to the wealth of both electronic and geometric information that can be extracted from them. Crucially, recent technological and methodological improvements, in particular the advent of X-ray free electron lasers (X-FELs), has led to a significant increase in the quality of the data and placed great emphasis on theory for understanding these experiments. Here I will present a critical review of resolving ultrafast processes using X-rays. This discussion will be illustrated with several recent examples of our work, including the luminescence quenching of a copper(I) phenanthroline complex [2], the electron-hole dynamics in ZnO and ligand rebinding dynamics of NO in myoglobin.

[1] C.J. Milne, T.J. Penfold, and M. Chergui. Coord. Chem. Rev., 227, 44-68.(2014).

[2] T.J. Penfold et al., J. Phys. Chem. A 117, 4591–4601 (2013).