Na_xAu and Cs_xAu bimetal clusters: Finite size analogs of sodium-gold and cesium-gold compounds

Mixed metal clusters of sodium and cesium with gold have been generated in a supersonic expansion from the mixed vapor phase. Their tendency towards binary cluster formation, relative thermodynamic stability, and ionization potentials have been experimentally and computationally investigated. The properties of the Na_xAu clusters may be understood within an electronic shell model based on delocalized cluster orbitals, whereas the characteristics of Cs_xAu are indicative of substantial ionic interactions. Relativistic density functional calculations have been performed to elucidate the cluster electronic structure and to rationalize observed properties which may not be accounted for by the jellium model. The properties of these finite-size clusters are shown to be related to the known bulk intermetallic compounds sodium-gold and cesium-gold (cesium aurid). respectively.