Ionization energies of Yn(n = 1−4)

We have studied the vertical ionization energies of yttrium clusters using complete active space multi-configuration followed by multi-reference configuration interaction calculations which included 2.7 million configurations. The computed ionization energies and the overall trend for the ionization potentials as a function of cluster size agree with the recent photoionization spectra of yttrium clusters reported by Knickelbein.