Ultrafast chemical bond studies by X-Ray Spectroscopy*

Among the most prominent ultrafast advances are the new capabilities of the X-ray Free Electron Lasers (XFELs). XFELs produce attosecond/femtosecond X-ray pulses providing a way to study ultrafast electronic processes in matter induced by X-ray photons [1,2]. A second XFEL pulse can be used in order to track the X-ray induced dynamics through X-ray Photoelectron Spectroscopy (XPS). When a core electron is removed from an atom or molecule it turns out into a core-hole state. Those core-hole states decay via Auger transitions. Every inner-shell ionization process is followed by an excitation in the valence resulting in additional states called satellite states. These states are close in energy to the main core-hole state, and it is expected that they have a high contribution in the XPS at the ultrafast regime. Our group collaborates in projects with experimental XFELs groups, providing theoretical support and developing numerical tools to simulate the dynamics of molecular systems. In particular, we have developed a semi-classical model that combines nuclear propagation with XPS calculations. The main objective of using this model is to study the dynamics of the electron together with the motion of the nucleus in molecules under the effect of XFEL pulses. So far, we are getting fairly accurate results for the carbon monoxide molecule and we hope to be able to extend our model to larger and complex systems. 

[1] A. Picón et al., Nat. Commun., 7 11652 (2016)

[2] S. Oberli et al., Phys. Chem. Chem. Phys., 21 25626 (2019)