X-ray-absorption spectra in KrF2 and FeCl2: Theory.

Abstract

Theoretical x-ray-absorption near-edge structure (XANES) and extended x-ray-absorption fine structure (EXAFS) of molecular and crystalline ${\mathrm{KrF}}_{2}$ and gas-phase ${\mathrm{FeCl}}_{2}$ have been obtained by using a modified X\ensuremath{\alpha} scattered-wave procedure. EXAFS calculations are made in the single-scattering approximation. Effects of multiple scattering near the absorption edge have been investigated by comparing predicted XANES and EXAFS spectra in the near-edge region. Two exchange-correlation potentials, X\ensuremath{\alpha} and energy-dependent Dirac (ED), were incorporated in the EXAFS calculations. Comparison between experimental and theoretical results confirm that the ED potential is more valid for EXAFS spectra. Molecular field splitting as well as resonance coupling were demonstrated by comparing the theoretical XANES of the isolated ${\mathrm{KrF}}_{2}$ molecule to that of ${\mathrm{FeCl}}_{2}$. The single-particle XANES calculation of molecular ${\mathrm{FeCl}}_{2}$ is compared with the experimental crystalline ${\mathrm{FeCl}}_{2}$ results of Stern.