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A: Atomphysik
A 4: Clusters I: Metal Clusters (joint session A and MO)
A 4.6: Vortrag
Montag, 2. April 2001, 17:00–17:15, H1012
Spectroscopic Properties of size-selected Alkali Atoms in Polar Molecule Clusters — •Christiana Bobbert1, Kenro Hashimoto2, C.P. Schulz1, and I.V. Hertel1 — 1Max-Born-Institut, Max-Born-Str. 2a, D-12489 Berlin, Germany — 2Computer Center and Department of Chemistry, Tokyo Metropolitan University, Tokyo, Japan
The spectroscopic properties of dissolved metals in liquids are well known. The electrons are completely detached from the alkali metal ions and exhibit spectroscopic properties on their own. To understand the basic chemical process of solvation on a microscopic scale, ionisation processes, spectroscopic properties and fragmentation of alkali metal atoms in a finite polar environment are of fundamental interest. We have chosen Na(H2O)n and Na(NH3)n as model systems. In spectroscopic studies the size dependent energy shift of the first electronically excited state has been determined. The excitation energy of Na(H2O)n drops from 16950 cm−1 for the bare sodium atom down to 9470 cm−1 for n=3. With increasing n>3 the absorption energy increases again and reaches 10566 cm−1 at n=12. The observed blue shift is in agreement with the absorption of solvated electrons in liquid water at 14100 cm−1. For Na(NH3)n the excitation energy shifts to the red with increasing n, reaches the value of solvated electrons in ammonia (6300 cm−1) at n=4 and remains almost constant for higher n. The excitation energy of Na(NH3)n clusters is qualitatively different from Na(H2O)n for clusters n>3, despite similar polar hydrogen-bond solvent molecules. Theoretical calculation based on the Na(H2O)n data reveal a interior structure.