Photoelectron spectra of thulium atoms encapsulated C₈₂ fullerene, Tm₂@C₈₂ (III) and Tm₂C ₂@C₈₂ (III)

Ultraviolet photoelectron spectra (UPS) and X-ray photoelectron spectra (XPS) of two thulium atoms and thulium-carbide cluster entrapped fullerenes, Tm₂@C₈₂ (III) and Tm₂C₂@C ₈₂ (III), were measured using synchrotron radiation and MgKα X-ray light sources. The UPS spectral onset energy of these endohedral fullerenes is around 0.9 eV, which is smaller than that of 1.2 eV of empty C₈₂. The UPS of Tm₂@C₈₂ (III) and Tm ₂C₂@C₈₂ (III) resemble each other. Further, the UPS of Tm₂@C₈₂ (III), Y₂@C₈₂-C _3v and Er₂@C₈₂-C_{3 v} are almost identical and as well as are Tm₂C ₂@C₈₂ (III), Y₂C₂@C ₈₂-C_3v and Er₂C₂@C ₈₂-C_3v. The XPS Tm4d_5/2 peaks of Tm₂@C₈₂ and Tm₂C₂@C₈₂ appear at higher binding energy region than that of Tm@C₈₂, which suggests the oxidation states of Tm atoms in Tm₂@C₈₂ (III) and Tm₂C₂@C₈₂ are higher than that in Tm@C₈₂.