Final Report Summary - XRAYONACTIVE (An X-ray spectroscopy view on active sites: removing the obscuring silent majority) Removing the silent majorityOne of the holy grails in catalytic research is the determination of the structure of the active site. Information on the catalytically active site is notoriously difficult to obtain as it concerns a small minority of states in a sea of other silent states. This silent majority of states obscures the action that takes place on the active states. X-ray absorption spectroscopy (XAS) is a powerful probe of the electronic structure and it can provide detailed information on systems under working conditions. Because XAS is a linear probe with respect to the number of atoms present, in most experiments the majority of non-active sites overwhelms the details from the active sites. We set out to use resonant inelastic x-ray scattering (RIXS) and tune the x-ray excitation to a specific site and as such are able to reveal its electronic in the RIXS plane. Using this approach we have demonstrated the presence of a few percent of oxide in a metallic system, an amount that is invisible to x-ray absorption spectroscopy.We have accidentally discovered that the angular dependent RIXS contain unexpected details that can be used to reveal details on the local orbital moments and the spin-orbit coupling. As a result we will further develop the 360 degree azimuthal scan RIXS technique, in combination with detailed calculations. The angular resolved RIXS techniques is a new tool for detailed electronic and magnetic structure determination of strongly correlated systems.The RIXS experiments on FeTiO3 revealed a new series of features that we attribute to metal-metal charge transfer channels. This will be further investigated with time-resolved experiments. In the near future a new x-ray technique will become available at x-ray free-electron lasers. These time-correlated two-photon excitation experiments will allow the combined time and energy mapping of the metal-metal charge transfer channels, thereby allowing a totally new view on the electron dynamics in FeTiO3 and related systems.We have developed open access software for the analysis of x-ray spectra (CTM4XAS), electronic structure analysis (CTM4DOC) and general data analysis (CTM4FIT). The usage of these programs by users around the world has triggered a large series of collaborations in the areas of bio-inorganic chemistry, strongly correlated systems, magnetism, actinide research, astrophysics, surface science and earth science.
