Photoelectron spectra of higher fullerenes and their potassium complexes

Abstract

Summary form only given. Higher fullerenes, C/sub 76/, C/sub 78/, C/sub 82/, C/sub 84/ and C/sub 96/ were isolated from carbon soot. Their ultraviolet photo election spectra (UPS) were obtained with a synchrotron radiation light source. The UPS of their potassium complexes were also measured. The UPS of pristine fullerenes can be divided into two parts, below and above 5 eV binding energy. The region above 5 eV is /spl pi/-like electron origin and /spl sigma/-like electrons contribute to the lower region. While the upper part differs from fullerene to another fullerene, the lower part is essentially identical. This suggests isoelectronic structures of skeletal carbon cages of fullerenes. The UPS of pristine fullerenes exhibit a strong intensity oscillation when the excitation photon energy has tuned. This intensity oscillation can be interpreted in terms of difference of the azimuthal quantum numbers which is deduced from a pseudo atom treatment of fullerenes. When potassium is dosed onto fullerenes, a formation of a new peak is observed in the UPS. The location of the new peak is between the Fermi level (E/sub F/) and the first band. This is due to an electron-filling from the potassium 4s level to the lowest unoccupied molecular orbital of fullerenes. Upon potassium dosing of the higher fullerenes the UPS spectral edge moves toward E/sub F/, but it does not cross E/sub F/, which indicates their semiconductive nature.