The orientation dependence of the core electron-energy loss of the carbon K edge in highly oriented pyrolytic graphite has been examined as a function of θ, the angle between the incident electron beam and the c axis normal to the basal plane of the graphite. The energy-loss spectra, detected in the reflection mode with a cylindrical mirror analyzer, show two major losses at 284.9 and 291.6 eV, corresponding, respectively, to the transition to the π and σ conduction band. The π loss has an angular dependence of (A+B ${\cos }^2$θ) while the σ loss has a dependence of (C-D ${\cos }^2$θ), where the coefficients A, B, C, and D are all positive. The angular dependence of the σ loss cannot be explained without including the contribution from the monopole transition from the C(1s) level to the 2s component of the ${\mathrm{sp}}^2$ orbitals of the σ band, thus indicating the breakdown of the dipole selection rule. The difference spectrum between two orientations shows that there is a second but weaker transition in the π loss at 287.2 eV. The line shape of the π loss is interpreted in terms of the configuration interaction between the core exciton (at ∼285 eV) with the π conduction states. The energy loss at 287.2 eV is assigned to the direct transition to the saddle point $Q_{2g}^{\mathrm{-}}$ in the π band.

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