Structural Evolution of Medium-Sized Gold Clusters. Aun- (n=36, 37, 38): Appearance of Bulk-Like Face Centered Cubic Fragment

We report a joint experimental and theoretical study of the structural evolution of medium-sized gold clusters. We find that the most stable structures of Au-36(-) to Au-38(-) exhibit core-shell type structures all with a highly robust tetrahedral four-atom core. All three clusters are observed to possess two coexisting isomers in the cluster beam. The appearance of a fragment of the face centered cubic (FCC) bulk gold, that is, the pyramidal Au-20(-), at the size of Au-38(-) implies that the cluster-to-bulk transformation starts to emerge at the medium size range. It is expected that larger pyramidal-like intermediates may emerge in later medium- to large-sized Au clusters beyond Au-38(-.)