L1andL3x-ray-absorption edges of iodine in AgI studied by multiple-scattering theory using complex potentials

The ${\mathit{L}}_1$ and ${\mathit{L}}_3$ x-ray-absorption edges of iodine have been measured in β- and γ-AgI at 11 K and in α-AgI at 460 K. Although the two nonsuperionic phases are characterized by different diffraction patterns, their absorption spectra are very similar. The edge fine structures of β and γ-AgI have been calculated by a full-multiple-scattering formalism utilizing a complex potential. The relevant characteristics of the spectra are satisfactorily reproduced by taking into account only the first two coordination shells of iodine, which are similar in β- and γ-AgI. This explains the similarity of the experimental spectra. Moreover, the main contribution to the calculated spectra comes from the iodine scatterers. This fact allowed us to calculate the main characteristics of I ${\mathit{L}}_3$ and I ${\mathit{L}}_1$ edges of α-AgI by taking into account only the first eight iodine atoms surrounding the absorber in the bcc iodine sublattice.