ON THE ROLE OF HIGH-ORDER MULTIPLE-SCATTERING TERMS IN BR K-EDGE XANES OF THE IONIC CONDUCTOR AGBR

The role of the multiple scattering terms in the Br K-edge X-ray absorption near edge structure (XANES) spectrum of AgBr is studied. In this system, in spite of the arrangement of atoms in collinear geometry, the first term in the expansion of the absorption coefficient (the single-scattering term) is shown to account for the main features of the experimental spectrum in the range of 80 eV above the absorption threshold. The role of both the large Br-Ag distance 0.289 nm and the short core hole lifetime in reducing the amplitude of multiple scattering terms is discussed. The size of the cluster of neighbor atoms probed by the XANES spectrum is studied: the second shell consisting of twelve Br atoms is shown to give the main contribution to the observed experimental features showing the minor role of the first coordination shell.