Bound delocalized excited states in I⁻ Xe_n clusters

By combining photoelectron spectra and photodetachment action spectra of I⁻ Xe_n clusters (n = 1–12), we have identified bound extended excited electronic states. The critical size to the binding of such states is n > 4–5. The spatial confinement and the binding energy of the excited states increase monotonously with the cluster size. We discuss the analogy between these bound electronic states and the binding of excess electrons in the Xe_n⁻ clusters. This study introduces a new methodology for the investigation of empty bands in clusters, residing above or below the vacuum level, via the excitation of slightly perturbing impurity states.