X-Ray photo- and resonant Auger-electron spectroscopy studies of liquid water and aqueous solutions

It has only recently become possible to use photoelectron spectroscopy (PES) to study the electronic structure of highly volatile aqueous surfaces. Here, we review current X-ray PES and related resonant Auger-electron decay and intermolecular Coulomb decay investigations in solution, which aim at understanding the solute–water, water–water, and solute–solute interactions at the microscopic level. Systems that will be discussed include neat liquid water, and aqueous solutions of hydroxide, hydronium, salts and amino acids. From observed chemical shifts in the main photoelectron lines or from the occurrence of spectator Auger-electron peaks, information on electron dynamics and/or energy transfer processes, and at times on the structure of the hydration complex, may be accessed. Furthermore, we discuss PES in conjunction with variable energy incident X-ray photons; with the resulting change of the (photo)electron kinetic energy, ion spatial distributions at the liquid–vapor interface can be determined.