Probing the Structural Evolution of Gold-Aluminum Bimetallic Clusters (Au₂Al_n^-, n = 3-11) Using Photoelectron Spectroscopy and Theoretical Calculations

We report a combined photoelectron spectroscopy and theoretical study of the structural evolution of aluminum cluster anions doped with two gold atoms, Au₂Al_n^- (n = 3-11). Well-resolved photoelectron spectra have been obtained at several photon energies and are used to compare with theoretical calculations to elucidate the structures of the bimetallic clusters. Global minima of the Au₂Al_n^- clusters were searched using the basin-hopping method combined with density functional theory calculations. Vertical detachment energies were computed for the low-lying isomers with the inclusion of spin-orbit effects and were used to generate simulated photoelectron spectra. Au₂Al₂^- was previously found to exhibit a tetrahedral structure, whereas Au₂Al₃^- is found currently to be planar. Beyond n = 3, the global minima of Au₂Al_n^- are dominated by three-dimensional structures. A robust square-bipyramidal Al₆ motif is observed for n = 6-9, leading to a highly stable tubular-like global minimum for Au₂Al₉^-. Compact three-dimensional structures are observed for n = 10 and 11. Except for Au₂Al₄^-, Au₂Al₆^-, and Au₂Al₇^-, the two gold atoms are separated in these digold-atom-doped aluminum clusters due to the strong Au-Al interactions.