Ultraviolet photoelectron spectra of mono-metal endohedral fullerene Er@C₈₂ (I)

Ultraviolet photoelectron spectra (UPS) of Erbium endohedral fullerene Er@C₈₂ (I) were measured using a synchrotron radiation light source. The spectral onset of Er@C₈₂ (I) was 0.4 eV, which is smaller than those of divalent atom endohedral metallofullerenes and analogous to those of trivalent atom endohedral metallofullerenes. The upper valence structure (E _b < 5 eV) of Er@C₈₂ (I) was almost identical with those of C_2v-Tb@C₈₂ and C_2v-La@C₈₂. The oxidation states of Er in Er@C₈₂ from the analogy of the oxidation state of Tb in Tb@C₈₂ and La in La@C₈₂ is estimated to be +3. The UPS of Er@C₈₂ (I) differs from those of Tm@C₈₂ isomers. The reason of the difference is attributed to differences in their cage structures and oxidation states. The upper valence UPS of Er@C₈₂ (I) could be well reproduced by a simulated spectrum obtained with a Gaussian03 program module assuming C₈₂-C_2v cage structure with three additional electrons.