Electron Affinities of Ligated Icosahedral M 13 Superatoms Revisited by Gas-Phase Anion Photoelectron Spectroscopy.

The electron binding energies of the ligand-protected gold/silver-based cluster anions, [Au 25 (SR) 18 ] - , [XAg 24 (SR') 18 ] 2- (X = Ag + , Au + , Pd 0 , or Pt 0 ), and [PdAu 24 (C≡CR″) 18 ] 2- having icosahedral M 13 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 Ag 13 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 PdAu 12 protected by Au 2 (C≡CR″) 3 units was much larger than that of PdAg 12 protected by Ag 2 (SR') 3 units.