Photoelectron Imaging Signature for Selective Formation of Icosahedral Anionic Silver Cages Encapsulating Group 5 Elements: M@Ag12− (M = V, Nb, and Ta)

An assembly of thirteen atoms is expected to be a distinctive nanocluster, as they can form highly symmetric architectures like those belonging to D3h, Oh, D5h, and Ih point groups. Among them, icosahedra are the best known as the iconic structures in the finite size regime. Here, using photoelectron imaging spectroscopy in combination with density functional theory (DFT) calculations, we present a simple yet convincing experimental signature for selective formation of icosahedral cages of anionic silver clusters encapsulating a dopant atom of group 5 elements: M@Ag12− (M = V, Nb, and Ta). Their photoelectron images obtained at 4 eV closely resemble one another, indicating that the doped clusters are all in valence iso-electronic systems. Most strikingly, only a single ring is observed, which is assignable to photodetachment signals from a five-fold degenerate superatomic 1D electronic shell in the 1S21P61D10 configuration of valence electrons. The perfect degeneracy of the 1D orbital represents an unambiguous fingerprint of an icosahedral symmetry, which would otherwise be lifted in all the other possible structural isomers. The experimental results are fully supported by DFT calculations, which reveal that icosahedral geometries with the spin multiplicity of singlet are the most stable forms for M@Ag12− (M = V, Nb, and Ta) and that D5h, Oh, and D3h structures are not found even in metastable states.