ELECTRONIC SHELL STRUCTURE IN THE IONIZATION-POTENTIALS OF COPPER CLUSTERS

The ionization potentials (IPs) of copper clusters (Cu(n)) up to 150 atoms have been bracketed using laser photoionization. Large decreases in IP at n = 2, 8, 20. 30, 34, 40 and 60 atoms are observed, as well as a strong odd-even alternation extending beyond 100 atoms. These features correspond to electronic shell and subshell closings predicted for systems of n valence electrons confined to spherical or spheroidal potentials. The decreases in IP expected to accompany shell closings at n = 58 and 92 are absent, however, and a new set of local extrema are observed, including local maxima at n = 57 and 88-91 and minima at n = 49 and 92. The possibility of perturbations to the electronic energy level structure due to geometric packing constraints is discussed.