X–ray Spectroscopy of Complex Chemical Systems in Liquid Phase

Modern light sources like synchrotron and free electron laser facilities provide highbrilliant, monochromatic and high coherent X–ray beam with tunable photon energiescovering almost the whole electromagnetic spectrum. These unique properties ofthe light sources enable to implement novel experimental methods for investigatingdynamical chemical processes.The atomic components of chemically relevant systems and solvents essentially consistof light elements. The chemical reactivity of these systems are primarily definedby their electronic configurations. Information about the electronic structure wouldelucidate the understanding of chemical processes and reactions on a fundamentallevel. This is one prerequisite to obtain a complete picture of the chemical characteristics.Aqueous solutions and isomerization processes are elemental phenomenain nature. However, the description of these mechanisms on the molecular level isnot complete.In this thesis, static and time–resolved X–ray spectroscopic methods are describedwhich have been developed and applied to investigate fundamental chemical interactionsof aqueous solutions and isomerization of molecules on the atomic scale.The work of my PhD thesis consists of designing and commissioning an experimentalend station including a detection device to perform the aimed experiments in liquidphase. The goal is to investigate ion–water interactions as well as isomerizationprocesses. By employing the X–ray spectroscopic technique, the unoccupied and occupiedorbitals are probed and information about the electronic configurations areobtained. Concerning the ion–water interaction, the results showed that the watermolecules are mainly influenced by the cation and that ion specific influences aremirrored in the electronic structure. Furthermore, the impact of ions is primarilylimited to water molecules in close vicinity. A significant difference between the firstsolvation shell and bulk water is observed.The results of the second phenomenon investigated have shown remarkable differencesin the electronic configuration of trans– and cis–azobenzene. Furthermore,with X–ray spectroscopy all electron–hole–pair final states are observed, includingthe optically dark states. This fundamental work might help to further elucidatethe dynamical pathways of the isomerization mechanism. Additionally, the firsttime–resolved soft resonant inelastic X–ray scattering (RIXS) experiment at a synchrotronwas carried out successfully in an optical pump and X–ray probe scheme.The future direction and the opportunities of this relatively young research field ofcomplex chemical systems in liquid phase will be addressed