Iron clusters and oxygen-chemisorbed iron clusters

The photoelectron spectroscopy of size-selected Fe-n(-) (n = 3-24) clusters and oxygen-chemisorbed clusters FenO- (n = 1-16), has been studied at 3.49-eV photon energy with a magnetic-bottle time-of-flight photoelectron spectrometer. While the spectra of the pure iron clusters show rather sharp features in the whole size range, those of the oxygen-chemisorbed species are considerably different, with extensive sharp structures observed for n only up to 6. The electron affinities (EAs) of both the bare and chemisorbed clusters exhibit strong size variations. However, the first oxygenation of the iron clusters induces a systematic lowering of EA in the size range n = 9-15. Towards a complete molecular picture of these interesting clusters, density-functional calculations are being performed to determine the equilibrium cluster structures, oxygen chemisorption sites, and their electronic structures. The equilibrium structures obtained for FenO with n = 2-6 are reported.