Multi-messenger X-ray Science – Electron Densities From a Combined Analysis of Elastic X-ray Scattering and X-ray Emission Data

Supervisors: Prof. Nina Rohringer (DESY, UHH), Jun.-Prof. Christina Brandt (UHH)

We propose an interdisciplinary project between the natural and mathematical sciences to develop novel x-ray data analysis methods for combined x-ray diffraction and x-ray emission spectroscopy measurements at high-brilliance x-ray sources. While coherent xray diffraction gives access to the structure (position of atoms) of a chemical compound or reaction unit, x-ray emission spectroscopy is a complementary and sensitive probe to the changes of the chemical bonds. The interpretation of the latter strongly relies on comparison with theoretically calculated spectra (electronic structure calculations). Pioneering experiments at storage-ring based x-ray sources and x-ray free electron lasers (XFELs) have shown the possibility for combining x-ray diffraction, x-ray scattering and x-ray emission spectroscopy in one high-quality experiment. Currently, the data analysis and reconstruction of the underlying physical quantities of interest (electron density, oxidation state, electron affinity, etc.) are undertaken independently from the two techniques. In the spirit of quantum crystallography, we propose to refine electronic structure (quantum chemistry) calculations by constraining the minimization problem of the total energy by measured x-ray structure factors and x-ray emission spectra. The goal is thus to predict the valence electron wave function by a combined theoretical and experimental method.