Design and implementation of a soft X-ray absorption spectroscopy setup for liquid samples at SwissFEL

This thesis presents the development and implementation of a novel experimental setup for time-resolved soft X-ray absorption spectroscopy on liquid samples at SwissFEL. The setup allows the investigation of important absorption edges, such as the nitrogen K-edge, the oxygen K-edge and transition metal L-edges, for site-selective studies of a sample in a single experiment. A key feature of the setup is a novel catcher design in combination with a gas-squeezing liquid jet. This allows the reliable use of liquid sheets of adjustable thickness in a high vacuum environment adhering to the requirements of experiments at free-electron laser sources. The setup can be operated with small sample volumes of 50 mL , and recircula- tion of the sample is possible. Test experiments at a synchrotron light source provided first valence absorption spectra of liquid water. At the X-ray free-electron laser, proof-of-concept experiments yielded absorption spectra of water around the oxygen K-edge and the transient absorption of a 30 mM aqueous iron(II)-trisbipyridine solution around the nitrogen K-edge and the iron L3-edge. Different modalities for X-ray absorption measurements with intense pulses from a free-electron laser were compared and recommendations depending on the sample conditions were formulated.