High-Resolution Core-Level Photoabsorption of Alkali Halides

Abstract

The X-ray Absorption Near Edge Structure (XANES) of single-crystal alkali halide salts have been measured at low temperature (T≈80 K). By employing the electron partial-yield detection technique, spectra of NaF, NaCI, 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 features at the absorption threshold and broader absorption features extending 50–80 eV above threshold. The high energy resolution of the soft X-rays (ΔE/E ≈ 4000) allowed the detection of previously unobserved fine structure, particularly in the near-edge region. The narrow features below and just above threshold are attributed to core-level excitons. The intense, broader peaks further above threshold are assigned to single-electron scattering resonances. An ab initio multiple-scattering calculation is used to model the latter effect. Contributions from atomic multielectron excitations, estimated by a comparison to the K-edge photoabsorption spectrum of Ne in the gas phase, are found to be very small.