Photoelectron spectra of metal fullerenes: Are metal fullerenes molecular crystals or not?

Ultraviolet photoelectron spectra (UPS) of GdC₈₂ and La₂C₈₀ were measured using synchrotron radiation. The specimens for the measurement were not evaporated films but drying up films obtained from the metal fullerene solutions. Although the effect of the contamination to the specimens remains even after heat treatment, the UPS of the GdC₈₂ film show several characteristic structures that are essentially identical to those of LaC₈₂. This suggests that the interaction between the GdC₈₂ molecules are small and GdC₈₂ can be treated as a molecular crystal. The spectrum of La₂C₈₀ differs from those of other fullerenes, which indicates either that the interaction among the La₂C₈₀ molecules are too large to give a sharp spectrum or that the molecule does not have so-called cage structure.