Electronic structure of C84 film studied by photoemission measurement and first-principles calculation

We have measured the photoemission spectra of a C-84 film (isomer mixture) with synchrotron radiation. The valence band exhibits abundant spectral features from the Fermi level to similar to 18 eV binding energy. The relative intensity between the lowest binding energy feature (labeled as A) and the next lowest binding energy feature ( labeled as B) oscillates distinctly within the experimental photon energy region from 21.0 to 63.0 eV. The energy levels and density of states (DOS) are calculated for the D-2d(23)-C-84 and four D-2 symmetric (D-2(1), D-2(5), D-2(21) and D-2(22)) C-84 isomers to help us to understand the electronic structure. The experimental features and the theoretical DOS peaks have one-to-one correspondence. The number of electrons occupying the states of feature A is 12 or 13.3, depending on the different kinds of isomer mixtures. The electron occupation of feature B is 18.67 e. With the spherical symmetric approximation, features A and B can be characterized with angular momenta of 6 and 5, respectively. The angular momentum difference is the reason for the photoelectron intensity oscillations.