The structural evolution of negatively charged gold clusters (Au(n)(-)) in the medium size range for n = 27-35 has been investigated using photoelectron spectroscopy (PES) and theoretical calculations. New PES data are obtained using Ar-seeded He supersonic beams to achieve better cluster cooling, resulting in well-resolved spectra and revealing the presence of low-lying isomers in a number of systems. Density-functional theory calculations are used for global minimum searches. For each cluster anion, more than 200 low-lying isomers are generated using the basin-hopping global minimum search algorithm. The most viable structures and low-lying isomers are obtained using both the relative energies and comparisons between the simulated spectra and experimental PES data. The global minimum structures of Au(n)(-) (n = 27, 28, 30, and 32-35) are found to exhibit low-symmetry core-shell structures with the number of core atoms increasing with cluster size: Au(27)(-), Au(28)(-), and Au(30)(-) possess a one-atom core; Au(32)(-) features a three-atom triangular core; and Au(33)(-) to Au(35)(-) all contain a four-atom tetrahedral core. The global searches reveal that the tetrahedral core is a popular motif for low-lying structures of Au(33)(-) to Au(35)(-). The structural information forms the basis for future chemisorption studies to unravel the catalytic effects of gold nanoparticles.

A variety of experimental techniques are used to resolve energetically close isomers of Au 7 − and Au 8 − by combining photoelectron spectroscopy and ab initio calculations. Two structurally distinct isomers are confirmed to exist in the cluster beam for both clusters. Populations of the different isomers in the cluster beam are tuned using Ar-tagging, O 2 -titration, and isoelectronic atom substitution by Cu and Ag. A new isomer structure is found for Au 7 − , which consists of a triangular Au 6 unit with a dangling Au atom. Isomer-specific photoelectron spectra of Au 8 − are obtained from O 2 -titration experiment. The global minimum and low-lying structures of Au 7 − , Au 8 − , and MAu n − ͑n =6,7; M=Ag,Cu͒ are obtained through basin-hopping global minimum searches. The results demonstrate that the combination of well-designed photoelectron spectroscopy experiments ͑including Ar-tagging, O 2 -titration, and isoelectronic substitution͒ and ab initio calculation is not only powerful for obtaining the electronic and atomic structures of size-selected clusters, but also valuable in resolving structurally and energetically close isomers of nanoclusters.

Golden cage: The two smallest anionic gold cages, Au16− and Au17−, are doped with a Cu atom to give the cluster anions CuAu16− (see picture) and CuAu17−, respectively. The photoelectron spectra of CuAu16− and CuAu17− suggest that the doping does not alter the structures of the parent cages. Theoretical studies confirm that the Cu atom resides in the center of the gold cages, similar to the situation with endohedral fullerenes.

The golden Au16− cage is doped systematically with an external atom of different valence electrons: Ag, Zn, and In. The electronic and structural properties of the doped clusters, MAu16− (M=Ag,Zn,In), are investigated by photoelectron spectroscopy and theoretical calculations. It is observed that the characteristic spectral features of Au16−, reflecting its near tetrahedral (Td) symmetry, are retained in the photoelectron spectra of MAu16−, suggesting endohedral structures with little distortion from the parent Au16− cage for the doped clusters. Density functional calculations show that the endohedral structures of M@Au16− with Td symmetry are low-lying structures, which give simulated photoelectron spectra in good agreement with the experiment. It is found that the dopant atom does not significantly perturb the electronic and atomic structures of Au16−, but simply donate its valence electrons to the parent Au16− cage, resulting in a closed-shell 18-electron system for Ag@Au16−, a 19-electron system for Zn@Au16− with a large energy gap, and a 20-electron system for In@Au16−. The current work shows that the electronic properties of the golden buckyball can be systematically tuned through doping.

The effects of isoelectronic substitution on the electronic and structural properties of gold clusters are investigated in the critical size range of the two-dimensional (2D)-three-dimensional (3D) structural transition (MAu(n)(-), n=8-11; M=Ag,Cu) using photoelectron spectroscopy and density functional calculations. Photoelectron spectra of MAu(n)(-) are found to be similar to those of the bare gold clusters Au(n+1)(-), indicating that substitution of a Au atom by a Ag or Cu atom does not significantly alter the geometric and electronic structures of the clusters. The only exception occurs at n=10, where very different spectra are observed for MAu(10)(-) from Au(11)(-), suggesting a major structural change in the doped clusters. Our calculations confirm that MAu(8)(-) possesses the same structure as Au(9)(-) with Ag or Cu simply replacing one Au atom in its C(2v) planar global minimum structure. Two close-lying substitution isomers are observed, one involves the replacement of a center Au atom and another one involves an edge site. For Au(10)(-) we identify three coexisting low-lying planar isomers along with the D(3h) global minimum. The coexistence of so many low-lying isomers for the small-sized gold cluster Au(10)(-) is quite unprecedented. Similar planar structures and isomeric forms are observed for the doped MAu(9)(-) clusters. Although the global minimum of Au(11)(-) is planar, our calculations suggest that only simulated spectra of 3D structures agree with the observed spectra for MAu(10)(-). For MAu(11)(-), only a 3D isomer is observed, in contrast to Au(12)(-) which is the critical size for the 2D-3D structural transition with both the 2D and 3D isomers coexisting. The current work shows that structural perturbations due to even isoelectronic substitution of a single Au atom shift the 2D to 3D structural transition of gold clusters to a smaller size.

Structural, electronic, and magnetic properties of the golden cage doped with a transition-metal atom, MAu 16 − ͑M = Fe,Co,Ni͒, are investigated using trapped ion electron diffraction, photoelectron spectroscopy, and density-functional theory. The best agreement to experiment is obtained for endohedral M @Au 16 − structures but with considerable distortions to the parent Au 16 − cage. Fe@ Au 16 − and Co@ Au 16 − are found to have similar structures with C 2 symmetry while a C 1 structure is obtained for Ni@ Au 16 −. The 4s electrons are observed to transfer to the Au 16 cage, whereas atomiclike magnetism due to the unpaired 3d electrons is retained for all the doped clusters.

We report a joint experimental and theoretical study on the structures of a series of gold clusters doped with a group-14 atom: MAu(x)(-) (M = Si, Ge, Sn; x = 5-8). Well-resolved photoelectron spectra were obtained and compared to calculations at several levels of theory to identify the low-lying structures of MAu(5-8)(-). We found that the structure of SiAu(5)(-) is dominated by the tetrahedrally coordinated Si motif, which can be viewed as built from the tetrahedral SiAu(4)(-) by an extra Au atom bonded to a terminal gold atom. However, SiAu(6)(-) and SiAu(7)(-) have quasi-planar structures, similar to those of GeAu(6)(-)/SnAu(6)(-) and GeAu(7)(-)/SnAu(7)(-), respectively. SiAu(8)(-) again has a tetrahedrally coordinated Si structure, which displays a structural motif of a dangling Au-Si unit sitting on a gold cluster surface, resembling that of the larger Si-doped gold cluster SiAu(16)(-). For M = Ge, Sn, our results show that the major isomers of GeAu(5-8)(-) have structures similar to those of the corresponding SnAu(5-8)(-) clusters, and they can be viewed as grown from the previously suggested square-pyramidal GeAu(4)(-) and SnAu(4)(-), respectively. Population of minor isomers was observed for SnAu(5)(-), GeAu(6)(-), SnAu(6)(-), and GeAu(8)(-). The 3D to quasi-2D to 3D structural evolution for SiAu(5)(-) to SiAu(8)(-) and the structural convergence for MAu(x)(-) (M = Si, Ge, Sn) at x = 6, 7 manifest competitions between the tendency of forming molecule-like structures around the group-14 dopant (optimizing M-Au interactions) and the strong tendency of forming planar structures for small gold anion clusters (optimizing Au-Au interactions).

The structural and electronic effects of isoelectronic substitution by Ag and Cu atoms on gold cluster anions in the size range between 13 and 15 atoms are studied using a combination of photoelectron spectroscopy and first-principles density functional calculations. The most stable structures of the doped clusters are compared with those of the undoped Au clusters in the same size range. The joint experimental and theoretical study reveals a new C(3v) symmetric isomer for Au(13)(-), which is present in the experiment, but has hitherto not been recognized. The global minima of Au(14)(-) and Au(15)(-) are resolved on the basis of comparison between experiment and newly computed photoelectron spectra that include spin-orbit effects. The coexistence of two isomers for Au(15)(-) is firmly established with convincing experimental evidence and theoretical calculations. The overall effect of the isoelectronic substitution is minor on the structures relative to those of the undoped clusters, except that the dopant atoms tend to lower the symmetries of the doped clusters.