Advances in research on clusters of transition metal atoms

Abstract

This article reviews research on the physical and chemical properties of clusters of transition metal atoms, with special emphasis on recent advances made through the new molecular beam and flow techniques. Following our introductory section describing motivation for the study of metal clusters, we outline the major synthetic techniques: Matrix isolation or suspension and free-jet or cold flow condensation of laser-vaporization plasmas. Before discussing the new experiments based on these methods, we review physical and chemical models of transition metal clusters. These models are adaptations of bulk or molecular descriptions of metals or metal containing compounds, and are concerned with the prediction of electronic structure and elementary excitation in clusters, magnetic order and structural rigidity, or chemical reactivity and perturbations. Within this framework we survey recent experimental measurements and their interpretations. Highlighted examples include: (1) the precision measurement of rovibronic or magnetic properties of dimers and trimers as tests of computational electronic structure approximations, (2) measurements of electron binding energies of Fe and Ni clusters as a probe of the molecular versus bulk behavior of these systems, (3) the current status of experiments on the optical properties of small metallic particles, (4) magnetic moment measurements on Fe clusters as critical tests of the molecular theory of metallic and magnetic behavior, (5) discussion of possible effects of cluster melting, and the melting of Au clusters, (6) the facile size-selected reactions of free Fe and Ni clusters with H 2, 0 2 and CO, and (7) the evidence for new chemistry in the adsorption of hydrocarbons on free Pt. Ir and Ru clusters.