Molecular Physics seminar

Water in the Atmosphere: A Spectroscopist’s View of the Aqueous Surface

by Clara Saak (Uppsala University)

FA 31 ()

FA 31

Water is abundant on Earth, but is rarely found in its pure form. Typically it exists as aqueous solutions in our environment containing solvated ions, as in oceans or in living organisms. The ability of water to form strong hydrogen bonds (HB) is thought to be the source of many of its unique properties, and it is speculated that the formation of a three-dimensional HB network is a crucial step in the early condensation behaviour of water droplets and aerosols in the atmosphere. However, interactions between water molecules and solvated ions can be markedly different at the surface of the droplets than in the bulk, leading to effects such as local surface enrichment or depletion of ions, enhanced ion pairing, layer formation, and partial desolvation of solutes. In this talk I present an overview of experiments performed in our group to investigate aqueous interfaces via surface sensitive X-ray photoelectron spectroscopy (XPS) and Auger measurements on samples ranging from a few molecules to the bulk liquid. In the first part I describe efforts to address the formation of HB networks in small pure water clusters via the ultrafast proton dynamics that follow after core ionisation. Beyond the water-water interaction in pure clusters, surface-sensitive XPS can also yield information on the influence of the water-ion interaction on e.g. sequential drying of sea-spray aerosols, leading to unexpected ion enrichment at the surface. Using the same technique we can also track surface enrichment as a function of temperature, which may provide insight on the mechanisms governing surface propensity. Overall, this work aims towards a fuller understanding of the fundamental interactions governing the rich, multifaceted behaviour of water in the atmosphere.