Photoelectron spectroscopy studies on the electronic, structural, and magnetic properties of small transition metal clusters

Clusters consisting of a few to few hundred atoms (∼2nm) cover a critical size range, in which the finite-sized systems evolve from molecular-like species to nano-particles. Gas-phase techniques are advantageous in probing this size range, permitting systematic examination of quantum size effects atom-by-atom without the influence of a substrate. Photoelectron spectroscopy of size-selected anions is a particularly powerful technique to provide cluster electronic structure information and follow the evolution from discrete molecular features to bulk band structures. Advances in our laboratory to improve the energy resolution of the photoelectron spectroscopic technique and to control the cluster temperatures have allowed us to obtain well-resolved electronic features of transition metal clusters with sizes more than one hundred atoms. This dissertation focuses on studies of four 3d cluster systems, Ti, Fe, Co, and Ni. Small clusters are shown to be molecular-like with discrete electronic transitions and dramatic size variations. Evidence is obtained for high symmetry clusters. Understandings are also achieved on the delocalization of d electrons by comparing the photoelectronic spectra and the magnetic moments of small clusters. For large clusters, the electronic density of states increase and bulk-like electronic features emerge. Comparisons of calculated density of states and electron affinities with experimental photoelectron spectroscopy data for Ti_n− and Ti_n clusters (n = 3–8, 13) as well as Fe _n− and Fe_n clusters (n = 2–8) lead to the assignments of the ground state structures for these clusters.