X-RAY-ABSORPTION NEAR-EDGE STRUCTURE AT THE FLUORINE-K EDGE IN CAF2 AND BAF2

A band-structure method has been developed for modeling the near-edge structure in fluorine K-edge x-ray absorption in CaF2 and BaF2. The co re-hole potential is included with a supercell technique. The model de scribes the main features of the experimental absorption spectra up to about 15 eV above the absorption threshold. The excitonic peak at the absorption threshold is followed by a series of peaks whose spacing c hanges in going from CaF2 to BaF2 by an amount consistent with electro n diffraction from crystal-lattice planes. The interpretation of the h igher-energy part of the absorption spectrum is complicated by possibl e multielectron excitations.