Ioniclike energy structure of neutral core-excited states in free Kr clusters

The development of electronic states in krypton clusters is investigated by high-resolution core-level electron spectroscopy. The energy ordering of bulk versus surface 3d-1np(n>5) core-excited states in neutral clusters is demonstrated to be reversed to the 3d-15p level situation. The cluster 3d-16p,7p states are proven to be at a lower energy than the corresponding atomic levels. These findings reveal the ioniclike energy structure of the neutral cluster core-excited levels. The phenomenon is explained by a spatial spread of the excited orbitals over the cluster lattice.