Electronic shell structure of group-IIIA metal atomic clusters

Ionization potentials of Alₙ and Inₙ clusters (n80) in supercooled beams have been measured by photoionization spectroscopy. The abrupt leveling near n=5 of the initial linear increase in ionization potentials and the subsequent gradual approach to the classical metallic sphere model are consistent with a simple picture of s-p band hybridization. For n>6, there is clear evidence of electron shell filling, yet substantial deviations from shell-model predictions remain. Crystal-field effects are considered the most probable source of symmetry breaking and give insight to cluster structure.