Ultraviolet photoelectron spectra of coinage metal clusters

Ultraviolet photoelectron spectra (UPS) were recorded for mass-selected negative clusters of copper (1–411 atoms), silver (1–60 atoms), and gold (1–233 atoms), using photodetachment lasers at 6.4 and 7.9 eV photon energy. The results provide a direct estimate of the vertical electron affinity (EA) of these clusters and information on the evolution of the d bands of copper and gold as a function of cluster size. The large even/odd alternation of EA in small clusters of these metals in earlier work is found to largely disappear as the cluster size exceeds 40 atoms. The ellipsoidal shell model is shown to be consistent with the observed EA behavior of all three metals, the predicted spherical shell closing at cluster 58 being evident for silver and gold. The UPS data show a smooth evolution of the d band toward that of the bulk metal.