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 can build up highly symmetric architectures like those belonging to D3h, Oh, D5h, and Ih point groups. However, an intuitive experimental signature that reveals their structural symmetries has been difficult to obtain. Here, using photoelectron imaging spectroscopy in combination with density functional theory calculations, we present simple yet convincing evidence for selective formation of icosahedral cages in 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: 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.