On the Magic Character of Al6Au-

Abstract

Joint experimental and theoretical studies have been carried out to identify the stability of aluminum gold clusters. The experimental studies where the AlnAu- clusters are generated via laser vaporization in a flow reactor and subsequently reacted with oxygen indicate that Al6Au- is an exceptionally stable species that is not only resistant to etching by oxygen but also grows in intensity when AlnAu- clusters are exposed to oxygen. Theoretical studies indicate that the six aluminum atoms in Al6Au- form an octahedron and that the Au atom occupies a hollow site above the triangular face of the octahedron. It is shown that it takes much larger energy to remove an Al or a Au atom compared to that for neighboring sizes, and this accounts for its resistance to oxygen. The special stability is rooted in the electronic spectrum that is marked by a large HOMO-LUMO gap of 1.38 eV, and the system is best described as a nearly free electron gas of 20 electrons.