Evolution of surface plasmon resonance absorption in large gas phase clusters of mercury: Approaching the bulk

We have advanced a new optical-absorption technique for the study of molecular-beam isolated clusters. For ${\mathrm{Hg}}_{\mathit{x}}$ clusters 2<x<200), the optical-absorption cross sections have been measured directly between 4.3 and 6.2 eV. With increasing cluster sizes a gradual enhancement of the absorption cross section at 5.93 eV is observed and discussed in terms of a surface plasmon resonance. The spectra of large clusters can be fitted quantitatively either by using the complex dielectric function of the metallic bulk material or by using the Mie-Drude imaginary part of the dynamic polarizability.