Electronic Structures and Chemical Bonding of Fluorinated Fullerenes Studied by NEXAFS, UPS, and Vacuum-UV Absorption Spectroscopies

The chemical bonding and the electronic structures of C 60 F x and C 70 F x were investigated by near edge X-ray absorption fine structure (NEXAFS) spectroscopy and UV photoemission spectroscopy (UPS), which are useful methods for examining the unoccupied and the occupied states, respectively. With these results and XPS measurements, we derived the electronic energy diagram of C 60 F x and discussed the change of the electronic structure from that of C 60 by fluorination. The energies of the LUMO and the Fermi level of solid C 60 F 48 were estimated to be −5.0 and −5.4 eV below the vacuum level, indicating that highly doped C 60 F x is a strong electron acceptor. The electronic absorption spectra of C 60 F x solutions deep into the vacuum-ultraviolet region were also measured, and the isomerism of C 60 F x was discussed by comparing the observed results with theoretical simulations.