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A: Atomphysik

A 1: Posters Monday (Cluster, Atoms in Fields)

A 1.10: Poster

Montag, 2. April 2001, 12:30–15:00, AT3

Electron Delocalization in Magnesium Clusters — •Thomas Diederich, Tilo Döppner, Josef Tiggesbäumker, and Karl–Heinz Meiwes–Broer — Fachbereich Physik, Universität Rostock, Universitätsplatz 3, 18055 Rostock

The formation of pure clusters from highly reactive metals can be achieved very effectively by the pick–up of atoms into superfluid helium droplets. We report on the experimental observation of small magnesium clusters produced by this method. For mass selection three ionization methods have been used: electron impact as well as nanosecond and femtosecond laser excitation.
Irrespective of the ionization method the mass spectra show the same characteristic features, i.e., steps, outstanding peaks and pronounced minima. This abundance distribution can be attributed to electronic shells, whereby the level order changes with increasing cluster size. A qualitatively derived dynamic shell model is capable to explain the experimental results. In addition, a phase transition to full electron delocalization is observed, which is completed at about 20 atoms.