Berlin 2005 – wissenschaftliches Programm
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O: Oberflächenphysik
O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)
O 15.4: Poster
Freitag, 4. März 2005, 17:00–20:00, Poster TU D
Interaction of Cs Halides with the surface of Solid Water between 80 and 200K. — •O. Höfft, A. Borodin, S. Bahr, and V. Kempter — Institut für Physik und Physikalische Technologien, TU Clausthal, Leibnizstr. 4, D–38678 Clausthal–Zellerfeld
The interaction of the Cs halides (CsX) with X=: F, Cl, and I with solid water was investigated with Metastable Impact Electron Spectroscopy (MIES) and UPS(HeI and II) and TPD between 80 and 200K. In MIES and UPS the emission from the outermost H2O MOs 1b1, 3a1, 1b2 and from the npX–states of X (n=2,3,5 for F, Cl and I, respect.) was monitored. We have prepared CsX/water interfaces, namely CsX layers on thin films of solid water and H2O adlayers on thin CsX films; they were annealed between 80 and 200K. At 80K closed CsX layers were obtained on H2O and vice versa; no interpenetration of the two components H2O and CsX could be observed. However, ionic dissociation of CsX takes place when H2O and CsX do interact directly. Above 105K we find that solvation of these ionic species becomes significant. Our results are compatible with a transition of ionic species from a surface site to an energetically favored water–separated site, where the species are solvated. Desorption of the water molecules, not involved in the solvation process, becomes sizeable above 135K. On the other hand, the temperature for desorption of H2O molecules interacting with salt ions depends strongly on the particular anion X− (120, 140, and 190K for F, Cl and I, respect.).