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

We have measured the photoemission spectra of a C₈₄ film (isomer mixture) with synchrotron radiation. The valence band exhibits abundant spectral features from the Fermi level to ∼18eV 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 63.0eV. The energy levels and density of states (DOS) are calculated for the D_2d(23)- C ₈₄ and four D₂ symmetric (D₂(1), D ₂(5), D₂(21) and D₂(22)) C₈₄ 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 18.67e. 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.