Probing the electronic structure of iron clusters using photoelectron spectroscopy

The electronic structure of small iron clusters, Fe(n)(-) (n = 3-34), was investigated using size-selected anion photoelectron spectroscopy at three photon energies: 355, 266, and 193 nm. Temperature-dependent studies were performed for selected clusters at 355 nm. The spectra of cold clusters at 355 nm revealed well-resolved electronic transitions. An unusually sharp threshold peak was observed for a number of clusters, particularly for n = 12-15, The electronic structure variations as a function of size were found to correlate well with changes in the cluster chemical reactivity in the same size ranges. The 193-nm photoelectron spectra, which provided a broader range of valence band electronic structures for the clusters, were compared to bulk photoemission spectra. The electronic structure revealed at 193 nm was found to exhibit bulk-like behavior starting at Fe(25). This observation was also consistent with the size dependence of the cluster electron affinities, ionization potentials, and chemical reactivity, which all showed more smooth size variations above Fe(25). It was also shown that the obtained electronic structure information from the well-resolved photoelectron spectra will be valuable to compare with and verify ab initio calculations in order to completely understand the chemical, structural, and magnetic properties of the iron clusters. (C) 2000 Published by Elsevier Science B.V.