THE MAGIC NUMBERS OF METAL AND METAL ALLOY CLUSTERS

Pure metal and metal alloy clusters including Cu(n), Ag(n), CunAgm, CunAlm, CunInm, AgnAlm, AgnInm, and CunPbm are produced by a gas aggregation source and investigated by time-of-flight mass spectrometry following ionization with a KrF excimer laser. In the case of pure metal clusters (Cu(n),Ag(n)In(n)), as well as alloy clusters composed of these metals, magic numbers are observed in their cluster ions which correspond to jellium shell closings (counting the total valence electrons from the component metals). These findings are in good agreement with their expected free-electron behavior. Interestingly, the abundance of pure Pb(n)+ corresponds to species which are expected to be especially stable due to their geometric structure. A similar situation also arises for the Pb-rich alloy clusters. By contrast, the metal alloy clusters CunPbm+ show magic numbers at jellium shell closing in the series of Cu-rich clusters.