Electronic-structure interactions in aqueous solutions: a liquid-jet photoelectron-spectroscopy study

This thesis reports how, by the development of the vacuum liquid‐microjet technique for photoelectron spectroscopy, electronic‐structure measurements have advanced to date. My focus is on measurements from transition‐metal aqueous solutions and from DNA components in water. Both systems are at the heart of current research activities worldwide, in fields including physical chemistry and biology, and aiming at a molecular‐level understanding of the interaction with the water solvent. For the metal solutions we apply direct and resonant photoelectron spectroscopy, enabling the determination of solutederived absolute binding energies and of the related reorganization energies of the respective redox pairs in water. We also obtain detailed and unique information on the electronic relaxation processes of core‐excited metal ions and of solvent molecules. The nature of the relaxation is a signature of the structure of the transition‐metal – water complex, and of accompanying ultrafast charge transfers between solute and solvent, and reverse. Naturally, our measurements also provide insight into the complex multi‐electron interactions in the aqueous environment, which are especially interesting for transition metal ions with incomplete 3d valence levels. I will show results of only few representative transition‐metal solutions out of the many others investigated during my research. The studies of biological relevant molecules mainly address valence energies of the individual building blocks of a given nucleotide. We are particularly interested in how the lowest ionization energy of a given nucleobase in water changes when adding the sugar and the phosphate, and how the results of bulk solvation compare with micro‐hydration. Resonant photoelectron studies from these latter systems have been only begun, and will be shortly described in view of electronic coupling between a molecule’s nitrogen atom and hydration water‐molecules. Future directions and challenges of this new field of photoelectron spectroscopy from solutes in their natural aqueous environment will be addressed. Abstract