Water-methanol solutions characterized by liquid $μ$-jet XPS and DFT; the methanol hydration case

Abstract: The advent of liquid $\mu$-jet setups as proposed by Faubel and Winter in conjunction with X-ray Photoemission Spectroscopy (XPS) has opened up a large variety of experimental possibilities in the field of atomic and molecular physics. In this study, we present first results from a synchrotron-based XPS core level and valence band electron spectroscopy study on water (10$^{-4}$M aqueous NaCl solution) as well as a water-methanol mixture using the newly commissioned ALBA liquid $\mu$-jet setup. The experimental results are compared with simulations from density functional theory (DFT) regarding the electronic structure of single molecules, pure molecular clusters, and mixed clusters configurations as well as previous experimental studies. We give a detailed interpretation of the core level and valence band spectra for the vapour and liquid phases of both sample systems. The resulting overall picture gives insight into the water-methanol concentrations of the vapour and liquid phases as well as into the local electronic structure of the pertinent molecular clusters under consideration, with a special emphasis on methanol as the simplest amphiphilic molecule capable of creating hydrogen bonds.