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Ultrafast Surface Chemistry and Catalysis with an X-ray Laser

I-29

Ultrafast Surface Chemistry and Catalysis with an X-ray Laser


M. Dell’Angela1

1Elettra Sincrotrone Trieste S.C.p.A., Trieste, Italy

The development of X-ray photon sources delivering femtosecond X-ray pulses, combined with the possibility of triggering chemical reactions by means of femtosecond lasers, pawed the way to the realization of the surface femtochemistry dream, i.e., the possibility to follow on a femtosecond timescale the evolution of the electronic structure during a chemical reaction at a surface. In this talk I will present two examples of ultrafast studies on catalytically relevant reactions at surfaces: CO desorption [1] and CO oxidation on Ru(0001) [2]. By employing as a probe X-rays pulses from the Linac Coherent Lighe Source (LCLS) X-ray free electron laser (FEL) and as a pump a femtosecond infrared laser synchronized with the probe, we have studied by means of time resolved X-ray emission (trXES) and time resolved X-ray absorption (trXAS) experiments the ultrafast evolution of bond distortions, weakening and breaking during the reactions. Thanks to the combination of trXAS, trXES and novel theoretical calculations, we successfully detected both transient intermediates but also the transition state region in the surface chemical reaction. Along with XES and XAS, time resolved photoemission spectroscopy (trPES) is an X-ray spectroscopy perfectly suited to reveal dynamical changes in the electronic structure. I will briefly discuss its applicability in surface femtochemistry experiments and the advantages of trXES and trXAS.

References:

[1] M. Dell’Angela, et al. Science 339, 1302 (2013).

[2] H. Öström, et al. Science 347, 978 (2015).