OPTICAL-EXCITATION IN SMALL IONIZED SODIUM CLUSTERS - CLOSED-SHELL AND OPEN-SHELL SYSTEMS

Photoabsorption cross-section profiles have been obtained for closed-shell and open-shell ionized size-selected sodium clusters Na9+, Na-21+ and Na11+. The spill-out of the valence electron cloud explains the red-shifted collective excitation frequency with regard to the Mie frequency. Quantum-mechanical calculations may give energy positions of the resonant structures consistent with the experiment. However, the absolute parameters of the profiles suggest that some oscillator strength is missing.