Au₃₄^-: A fluxional core-shell cluster

Among the large Au_n^- clusters for n > 20, the photoelectron spectra of Au₃₄^- exhibit the largest energy gap (0.94 eV) with well-resolved spectral features, making it a good candidate for structural consideration in conjunction with theoretical studies. Extensive structural searches at several levels of density functional and ab initio theory revealed that the low-lying isomers of Au₃₄^- can be characterized as fluxional core-shell type structures with 4 or 3 inner atoms and 30 or 31 outer atoms, i.e., Au₄@Au₃₀^- and Au₃@Au₃₁^-, respectively. Detailed comparisons between theoretical and photoelectron results suggest that the most probable ground state structures of Au₃₄^- are of the Au ₄@Au₃₀^- type. The 30 outer atoms seem to be disordered or fluxional, giving rise to a number of low-lying isomers with very close energies and simulated photoelectron spectra. The fluxional nature of the outer layer in large gold clusters or nanoparticles may have important implications for their remarkable catalytic activities. © 2007 American Chemical Society.