Electron Affinities of Ligated Icosahedral M13 Superatoms Revisited by Gas-Phase Anion Photoelectron Spectroscopy

The electron binding energies of the ligand-protected gold/silver-based cluster anions, [Au25(SR)18]-, [XAg24(SR')18]2- (X = Ag+, Au+, Pd0, or Pt0), and [PdAu24(C≡CR″)18]2- having icosahedral M13 superatomic cores, were reexamined by gas-phase photoelectron spectroscopy (PES) on a significantly intensified mass-selected ion beam. Laser fluence-dependent PE spectra and pump-probe PES revealed that the previous PE spectra were contaminated by PE signals due to the two-photon electron detachment via long-lived photoexcited states. Although the adiabatic electron affinities (AEAs) of the corresponding oxidized forms were found to be 1-2 eV larger than those previously reported, the effects of doping and ligation were not qualitatively affected. (1) The AEA of the Ag13 superatom (∼4 eV) was not appreciably affected by doping a Au atom at the center but was reduced by ∼2 eV by doping Pd or Pt, and (2) the AEA of PdAu12 protected by Au2(C≡CR″)3 units was much larger than that of PdAg12 protected by Ag2(SR')3 units.