Licentiate Seminar; Surface Enrichment and Proton Dynamics in Aqueous Systems Studied by Photoelectron Spectroscopy

This thesis seeks to contribute to the understanding of aqueous solutions, in particular to how interaction between water molecules and solvated ions or molecules give rise to various phenomena at the interface. The results can conceptually be arranged into two groups: photo-induced dynamics associated to the hydrogen bonding, and surface segregation phenomena relevant to e.g. atmospheric science.

These effects were studied using synchrotron based Soft X-Ray Photoelectron spectroscopy, supported by simulation and vibrational spectroscopy.

The first part,  concerns post-ionisation dynamics in pure water, in which proton transfer along the hydrogen bond axis plays a key role. The isotope dependent influence of this proton transfer on the decay pathways can be used to infer information on the strength of the intermolecular hydrogen-bonding network.  Understanding the nature of the hydrogen bond is a critical step in understanding water in isolation and in solution, as it is next to dipole interactions the main mechanism for intermolecular bonding with solutes.

The second part, concerns the surface composition of dry and wet systems of atmospheric relevance. We show that surface composition of solutions can be very different depending on the specific conditions of the system. We will show, that temperature, pH and relative humidity have a pronounced influence of on the surface enrichment of ions and molecules.

These results highlight the importance of a detailed understanding of the molecular processes governing surface enrichment.

Any changes in the aerosols surface composition will not only directly affect the rate of catalytic surface reactions, but will also influence the ability of the particle to act as a condensation nucleus.