ELECTRON-ENERGY-LOSS SPECTRA OF CRYSTALLINE C84

Transmission electron-energy-loss spectra of crystalline C84 have been measured and compared with those of C60, C70, and graphite. Two peaks due to the pi plasmon and the pi+sigma plasmon have been observed at 6.1 and 25.5 eV, respectively. The structures due to pi-->pi* transitions of C84 are much broader than those of C60 and C70 because of the lower molecular symmetry of C84. The energy of the interband transition between the highest occupied molecular orbitals and the lowest unoccupied molecular orbitals (band gap) was found to be 1.2 eV from the onset energy in the imaginary part epsilon2 of the dielectric function.