The third chapter describes the doping effect on the eight-electron superatoms based on anion photoelectron spectroscopy (PES) of a representative gold superatom and heterometal-doped silver-based superatoms. The electron binding energies of the representative superatom [Au25(PET)18]− (PET = 2-PhC2H4S) were reexamined by anion 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. Anion PES on silver-based superatoms [MAg24(DMBT)18]‒ (M = Ag, Au), [MAg24(DMBT)18]2‒ (M = Pd, Pt) having icosahedral MAg12 cores with 8 electrons showed that the electron affinity of the neutral Ag13 superatom (∼4 eV) was not appreciably affected by doping Au atom at the center but was reduced by ~2 eV by doping Pd or Pt. The doping effect can be rationalized by the charging effect and the two-step jellium potential.