Heidelberg 2015 – wissenschaftliches Programm

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UP: Fachverband Umweltphysik

UP 4: Postersession Atmosphäre

UP 4.25: Poster

Mittwoch, 25. März 2015, 10:45–19:45, G/Foyer

Studying Ice-crystallization on the Molecular Level using Nonlinear Optical Spectroscopy — •Ahmed Abdelmonem, Johannes Lützenkirchen, and Thomas Leisner — Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany

Heterogeneous ice formation on mineral surfaces is important for precipitation formation in mixed phase clouds and for the formation of cirrus clouds. It is not well understood which structural and chemical characteristics of ice nucleation surfaces and dissolved ions account for the variability in ice crystallization efficiency.

We apply Second Harmonic Generation (SHG) spectroscopy to monitor the evolution of water structuring at solid surfaces upon cooling down to the temperature of heterogeneous freezing. This method enables a direct discrimination between good and poor ice nucleating surfaces. In this presentation, we compare the evolutions of the freezing process of water on two different surfaces (sapphire and mica). In addition, a direct comparison between ice crystallization on sapphire surface in the presence and absence of dissolved salts is presented. While sapphire which is known as poor ice nucleator shows no influence on the structure of water molecules in contact with its surface upon cooling until the freezing point, mica which is one of the common ice nucleation atmospheric substances shows an increase in the local ordering of the first water layer in contact with the surface which is expected to facilitate and control the crystallization of ice at the surface.