Elucidating the Doping Effect on the Electronic Structure of Thiolate-Protected Silver Superatoms by Photoelectron Spectroscopy.

Gas-phase photoelectron spectroscopy (PES) was conducted on [XAg (SPhMe ) ] (X=Ag, Au) and [YAg (SPhMe ) ] (Y=Pd, Pt), which have a formal superatomic core (X@Ag ) or (Y@Ag ) with icosahedral symmetry. PES results show that superatomic orbitals in the (Au@Ag ) core remain unshifted with respect to those in the (Ag@Ag ) core, whereas the orbitals in the (Y@Ag ) (Y = Pd, Pt) core shift up in energy by about 1.4 eV. The remarkable doping effect of a single Y atom (Y=Pd, Pt) on the electronic structure of the chemically modified (Ag@Ag ) superatom was reproduced by theoretical calculations on simplified model systems and was ascribed to 1) the weaker binding of valence electrons in Y@(Ag ) compared to Ag @(Ag ) due to the reduction in formal charge of the core potential, and 2) the upward shift of the apparent vacuum level due to the presence of a repulsive Coulomb barrier between [YAg (SPhMe ) ] and electron.