3.1 Dynamics of Condensed Phase Molecular Systems

How acids and bases react in water is a question raised since the pioneering days of modern chemistry. With ultrafast spectroscopy it has been shown that the elementary steps in aqueous proton transfer occur on femtosecond to picosecond time scales. Aqueous acid-base neutralization predominantly proceeds in a sequential way via water bridging acid and base molecules. Soft-x-ray absorption spectroscopy (XAS), probing transitions from inner-shell levels to unoccupied molecular orbitals, is a tool to monitor electronic structure with chemical element specificity. The aim is now to develop steady-state and time-resolved soft-x-ray spectroscopy of acids and bases in water-poor and water-rich solutions. Here novel liquid flatjet technology is utilized with soft-x-ray sources at synchrotrons as well as table-top laser-based high-order harmonic systems, to elucidate the electronic structural evolution of proton transfer pathways. Questions to be solved are electronic structural changes upon hydrogen bond formation, the nature of hydrated proton species, and the impact of conversion from acid to conjugate base (or base to conjugate acid) in aromatic alcohols, carboxylic and amine compounds, and ultimately the oxygen oxidation state in hydrated protons.