NEAR-EDGE SODIUM AND FLUORINE K-SHELL PHOTOABSORPTION OF ALKALI-HALIDES

The x-ray-absorption near-edge structure (XANES) spectra of single-crystal alkali halide salts have been measured at low temperature (T almost-equal-to 80 K) with high resolution in energy. By employing the electron partial-yield detection technique, spectra of NaF, NaCl, and NaBr were obtained near the sodium K edge and spectra of LiF, NaF, and KF were obtained near the fluorine K edge. All spectra showed sharp absorption features at the absorption threshold and broader features extending 50-80 eV above threshold. Some narrow features close to threshold are attributed to core-level excitons. Contributions from atomic multiple-electron excitations, estimated by a comparison to the K-edge photoabsorption spectrum of Ne in the gas phase, are found to be very small. Thus, the intense broader peaks observed further above threshold arise from single-electron scattering resonances. These highly structured spectra of well-characterized ordered crystals provide a set of standard data which is used to test the multiple-scattering x-ray-absorption code FEFF V. For some spectra, at photon energies more than almost-equal-to 10 eV above threshold, the calculations achieve very good agreement with experiment. The dependence of the calculation on cluster size, order of scattering, and choice of self-energy is demonstrated.