Photoelectron spectroscopy of europium-silicon cluster anions, EuSin- (3≤n≤17)

We report the photoelectron spectra of EuSin- cluster anions (3 <= n <= 17). They reveal dramatic electronic rearrangements over the size range n=10-12. In particular, a marked increase in the adiabatic electron affinity of EuSi12 (2.8 eV) compared to its stoichiometric neighbor, EuSi11 (1.9 eV), is observed. We propose that a significant geometric reorganization due to the encapsulation of a europium atom occurs in this size range and is responsible for the detected changes in the electronic structure. In light of this interpretation, EuSi12 is the smallest fully endohedral europium-silicon cluster. (C) 2008 American Institute of Physics.