Microscopic structure of the plasma resonance in charged potassium microclusters

The dipole strength function of ${\mathrm{K}}_9^{+}$, ${\mathrm{K}}_{21}^{+}$, and ${\mathrm{K}}_{22}^{2+}$ charged microclusters is calculated within the framework of the random-phase approximation. Contrary to the case of neutral clusters, essentially no Landau damping is found in the systems under study here, the spectrum being dominated by a single peak carrying most of the oscillator strength. The coupling of the plasmon to thermal fluctuations of the surface can account for about 60% of the observed spreading width.