Anisotropy of the photoelectron mean free path and its influence on the EXAFS amplitude

The anisotropy of the inelastic mean free path (MFP) for electrons with energies between approximately 10-1000 eV has been studied for the first time in ReO₃, NaWO₃ and TiO crystals. The MFP was calculated within the one-plasmon and local density approximations from the imaginary part of the complex energy-dependent exchange and correlation potential of the Hedin-Lundqvist type. It is shown that the MFP in compounds with a highly anisotropic electron density distribution, such as ReO₃ and NaWO ₃, differs in various crystallographic directions from the MFP calculated for the averaged electron density. In particular, it was found that in the ReO₃ crystal, the MFP values in (100) directions coincide with those for a spherically averaged cluster potential and are approximately 1 AA smaller than in (110) and (111) directions. This result explains the variation of the outer shell amplitudes in the Re L₃-edge EXAFS in ReO ₃.