Electron-energy-loss spectra of crystallineC84

Transmission electron-energy-loss spectra of crystalline ${\mathrm{C}}_{84}$ have been measured and compared with those of ${\mathrm{C}}_{60}$, ${\mathrm{C}}_{70}$, and graphite. Two peaks due to the π plasmon and the π+σ plasmon have been observed at 6.1 and 25.5 eV, respectively. The structures due to π→${\mathrm{\pi }}^{\mathrm{*}}$ transitions of ${\mathrm{C}}_{84}$ are much broader than those of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ because of the lower molecular symmetry of ${\mathrm{C}}_{84}$. 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 ${\mathrm{\epsilon }}_2$ of the dielectric function.