Iron Clusters And Oxygen-Chemisorbed Iron Clusters

The photoelectron spectroscopy of size-selected${\rm{Fe}}_n^-$(n=3–24)clusters and oxygen-chemisorbed clustersFenO−(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 rangen=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 forFenOwithn=2–6are reported.