Transition to plasmonlike absorption in small Hg clusters

Optical absorption spectra for mass-selected ${\mathrm{Hg}}_{\mathit{n}}^{+}$ and ${\mathrm{Hg}}_{\mathit{n}}^{++}$ clusters show an abrupt transition to a collective, plasmonlike absorption as a function of increasing cluster size. The position of the single observed plasmon maximum is independent of the charge state and nearly independent of cluster size. The peak positions agree well with those of the classical Mie plasmon calculated from the experimental dielectric function. The width of the plasmon resonance is discussed and a strong temperature effect is conjectured.