We have investigated the orientation dependence of the structure near the boron $K$ edge in electron-energy-loss spectra from hexagonal boron nitride. Angular distributions of spectra recorded from crystals with $c$ axis tilted at 45° to the beam allow us to determine unambiguously the $\pi$ and $\sigma$ character of the final states at different energies. Results are in quantitative agreement with a model based on hydridized atomic orbitals.

• Received 4 December 1978

DOI:https://doi.org/10.1103/PhysRevLett.42.1361