The evolution of electronic structure in AlnCom

The ionization potentials of Al_nCo_m clusters (n>m) have been bracketed using laser photoionization mass spectrometry. We find the electronic shell structure manifested in the ionization potentials of Al_n for n≥7 is observed also for Al_nCo and Al_nCo₂, and is consistent with cobalt contributing one electron to the conduction band of the cluster. However, with increasing number of cobalt atoms, this simple picture breaks down; all vestiges of aluminum cluster electronic shell structure are absent for m≥4.