Indirect interband transitions in graphite with a wide quasigap

Sets of fundamental optical functions in the energy range of 0–40 eV for longitudinal indirect interband transitions in graphite with a quasi-gap up to 2.6 eV have been determined for the first time. Their structure and parameters depend strongly on the electron wave vector transfer q. The nature of the peaks and shoulders of these functions is explained within the model of theoretical shifted bands for four electron wave vector transfers q in a volume characteristic electron-energy losses for the Γ-P direction in the Brillouin zone. The calculations were performed on the basis of the known experimental volume characteristic electron-energy loss spectra of graphite in the range of 0–40 eV for |q| = 0.00, 0.375, 0.625, and 1.00 A−1 using a special software package.