Hannover 2013 – scientific programme
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MO: Fachverband Molekülphysik
MO 14: Poster 1: Cluster, Femtosecond Spectroscopy
MO 14.26: Poster
Tuesday, March 19, 2013, 16:00–18:30, Empore Lichthof
Hints at Glass Transitions in Free Water Clusters — •Adam Piechaczek1, Martin Schmidt2, and Bernd von Issendorff1 — 1Fakultät für Physik, Universität Freiburg, Germany — 2Laboratoire Aimé Cotton, Université Paris Sud, France
We studied caloric curves of free water clusters with different charge centers by nanocalorimetry. We observed transitions, indicated by pronounced excess heat capacities that vary with cluster size and the type of impurity. The transition temperatures as well as their extrapolations towards the bulk are close to glass transitions known for bulk-water and water in nanopores, but they are far below any melting and freezing points known for water under various conditions like crystalline structure, pressure and different types of confinements or impurities.
For most of the investigated impurities, we observed an increase of the transition temperatures with cluster size, which fits well to the concentration dependence of glass transitions in various dilute aqueous solutions. An exception is the aniline+-water system. Here, the size dependence is less pronounced. The location of the charge center, which is in this case on the aniline molecule outside of the water cluster, might be responsible for observed difference.
We applied two different techniques of nanocalorimetry. We use photo-excitation calorimetry for water clusters with excess electron and for those with the charging impurities O2− and aniline+. We excited protonated water clusters that do not provide sufficient photo-absorption cross-sections by multi-collisions with rare gas atoms.