OPTICAL PLASMON LOSSES IN STABILIZED AU-55 CLUSTERS

Au55 cluster compounds are investigated by optical spectroscopy and TEM. The optical spectra appear to be rather structureless, neither showing a collective excitation resonance nor exhibiting distinct absorption bands known from lower nuclearity clusters. We discuss changes of the electronic properties compared to larger Au clusters affecting both, 6sp electrons and 5d-6sp interband transitions, the cluster-ligand - interaction being considered as a charge transfer process. We additionally report on a low temperature instability of the cluster compound, which results in changed optical extinction spectra. A characteristic absorption feature at lambda = 400 nm is attributed to small, ligand-free Au cluster fragments.