In the 2nd period we have concluded the three activities described within EDAX and have been able to broaden even the scope of systems significantly, as already indicated in the previous reports. Thanks to the excellent scientists and PhD students scientific staff within EDAX. These are:
- “Proof-of-principle of Anti-Stokes RIXS as a superior probe of excited state dynamics and soft X-ray 4 wave mixing for multi-centre dynamics at an atomic scale at the existing brilliant Free-Electron Laser facilities (FLASH, Germany; FERMI, Italy; LCLS, USA) with a compact transportable set-up.”
- “Establish optimum conditions with transform limited pulses and a dedicated set-up at the European XFEL with unprecedented brilliance for Anti-Stokes RIXS and resonant soft X-ray 4 wave mixing.”
- “Derive complementary potential energy surfaces and excitations from sub-natural linewidth RIXS at the Swiss Light Source and €RIXS at the European Synchrotron Radiation Facility. At the Synchrotron BESSY Germany static RIXS, kinetics and driven phases.
The highly successful approach was to map out potential energy surfaces along selected coordinates, which we published in a series of publications. In particular for water as highly relevant solvent of our excited state molecules significant progress has been made. In the final period, we have been able to significantly enhance our understanding of the compatibility of continuous distribution models in liquid water at ambient conditions, highly relevant as the solvent of our photochemically active solutes.
Publications on solution situations as well as crystalline condensed phases have been continuously put forward and even after the project end we will continue to publish material based on the potential mapping approach. Having established this solid basis on the potential mapping approach for the static molecules/materials gives us great certainty, that the combination of potential energy surface mapping for excited states at European XFEL is a powerful excited state dynamcis tool. Computational science colleagues and the EDAX PI have written an invited “Review of Modern Physics” on “Dynamics of resonant X-ray and Auger scattering”, making many of these insights and approaches of EDAX available to a larger scientific community.
At BESSY, Germany we have both characterized with low resolution Fe based complexes, Proton and charge transfer systems with regard to their electronic structure, their long-time kinetics and their response to chemical variation such as pH dependence. In particular strongly improved experimentation due to the gained experience of the involved scientists with picosecond temporal resolution allows to characterize excited state behaviour of molecular and solids highly efficiently with soft X-ray spectroscopic approaches, in particular RIXS. Based on the experimental count rates achieved, we try to establish, if even at the Synchrotron radiation source Anti-Stokes RIXS could be possible, which would open the approach significantly independent of FEL sources. We have termed this campaign EDAX@VSR at the BESSY Synchrotron radiation source. With R. Büchner a PhD student significantly advanced our understanding beyond the Fe-based complexes towards photoexcitation in Porphyrins, where in particular the established Gouterman-model has been reformulated based on the balance of local central charge and covalent ligand rearrangement. R. Büchner handed in the thesis at the EDAX end and defends in spring 2022.
