Special CPM/CSC Seminar

Using time-resolved X-ray spectroscopy to probe electronic and structural dynamics in everything from proteins to nanoparticles to molecules in solution

Chris Milne

Paul Scherrer Institut

Using x-ray absorption spectroscopy (XAS) and x-ray emission spectroscopy (XES) to probe laser-excited samples we can obtain excited-state structural and electronic information on dynamics not available through other techniques.[1,2] One of the restrictions of most synchrotron-based implementations of this technique is the three-orders of magnitude mismatch between x-ray and laser repetition rates (MHz Vs. kHz). By using a laser capable of generating significant pulse energies at MHz repetition rates we can eliminate this discrepancy, thus greatly reducing measurement times and enhancing achievable signal-to-noise ratios.[3] Several examples that demonstrate the strength of this technique will be presented, including probing the electron relaxation in photoexcited TiO₂[4] and ZnO nanoparticles in solution, and resolving the dynamical structural changes associated with ligand rebinding in the protein myoglobin under physiological conditions. The ability to extend these types of measurements into the femtosecond regime at the SwissFEL hard X-ray free electron laser (XFEL), which is under construction at the Paul Scherrer Institute (Switzerland)[5], will be discussed.

[1] C. J. Milne, T. J. Penfold, and M. Chergui, Coordination Chemistry Reviews (2014) DOI:10.1016/j.ccr.2014.02.013.
[2] T. J. Penfold, C. J. Milne, and M. Chergui, Advances in Chemical Physics 153, 1 (2013).
[3] F. A. Lima, C. J. Milne, D. C. V. Amarasinghe, M. H. Rittmann-Frank, R. M. van der Veen, M. Reinhard, V.-T. Pham, S. Karlsson, S. L. Johnson, D. Grolimund, C. Borca, T. Huthwelker, M. Janousch, F. van\ Mourik, R. Abela, and M. Chergui, Rev Sci Instrum 82, 063111 (2011).
[4] M. H. Rittmann-Frank, C. J. Milne, J. Rittmann, M. Reinhard, T. J. Penfold, and M. Chergui, Angew. Chem. Int. Ed. 53, 5858 (2014).
[5] http://www.psi.ch/swissfel/.