Symmetry and electronic structure of noble-metal nanoparticles and the role of relativity -: art. no. 093401

We present high resolution UV-photoelectron spectra of cold mass selected Cu-n(-), Ag-n(-), and Au-n(-) with n=53-58. The observed electron density of states is not the expected simple electron shell structure, but is strongly influenced by electron-lattice interactions. Only Cu-55(-) and Ag-55(-) exhibit highly degenerate states. This is a direct consequence of their icosahedral symmetry, as is confirmed by density functional theory calculations. Neighboring sizes exhibit perturbed electronic structures, as they are formed by removal or addition of atoms to the icosahedron and therefore have lower symmetries. Gold clusters in the same size range show completely different spectra with almost no degeneracy, which indicates that they have structures of much lower symmetry. This behavior is related to strong relativistic bonding effects in gold, as demonstrated by ab initio calculations for Au-55(-).