Fragmentation of the photoabsorption strength in neutral and charged metal microclusters

The line shape of the plasma resonance in both neutral and charged small sodium clusters is calculated. The overall properties of the multipeak structure observed in the photoabsorption cross section of spherical ${\mathrm{Na}}_8$ and ${\mathrm{Na}}_{20}$ neutral clusters can be understood in terms of Landau damping. Quantal configurations are shown to play an important role. In the case of charged ${\mathrm{Na}}_9^{+}$ and ${\mathrm{Na}}_{21}^{+}$ clusters a single peak is predicted that carries most of the oscillator strength.