Copper clusters: The interplay between electronic and geometrical structure

Copper clusters in the 50- to 100-atom size range are found to exhibit electronic shell structure as well as icosahedral geometry. Clusters corresponding to filled shells have minimum intensity in near-threshold photoionization mass spectra, implying that they have locally higher ionization potentials than other cluster sizes. The chemical stability of these clusters is illustrated by a reduced reactivity towards O2. Cluster geometry is probed via the equilibrium reactions with H2O: Clusters having one copper atom more than closed icosahedral subshells show an enhanced binding of water. The relative importance of electronic and geometrical structure in determining cluster chemical properties is discussed.