Berlin 2015 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 23: Interfaces and Thin Films I (joint session CPP, DS)

CPP 23.7: Talk

Tuesday, March 17, 2015, 11:45–12:00, C 243

Extreme Surface Propensity of Halide Ions in Water — •Ellen H.G. Backus¹, Lukasz Piatkowski², Zhen Zhang¹, Huib J. Bakker², and Mischa Bonn¹ — ¹Max Planck Institute for Polymer Research, Mainz, Germany — ²FOM Institute AMOLF, Amsterdam, the Netherlands

The dominant part of water on earth is not pure water; it contains salts. Moreover, especially in atmospheric chemistry the ions present at the interface are important for various reactions occurring at these interfaces. These ions are potentially reactive and/or determine the water structure, thereby influencing the surface reactivity. Experimentally, it is very challenging to determine the local concentration of ions in the outermost molecular monolayer region of aqueous solutions. Here, we show how two-dimensional sum frequency generation spectroscopy can be used to determine this concentration by measuring the energy transfer rate between water molecules. The presence of ions leads to a reduction of this transfer rate. The data reveal a high surface propensity for iodide anions corresponding to a surface concentration three times higher than the bulk concentration.