ATOMIC-XAFS AND XANES

X-ray-absorption near edge structure (XANES) poses many theoretical ch allenges and a general quantitative theory remains elusive. We have st udied structural contributions to XANES based on high-order multiple-s cattering (MS) calculations, including X-ray polarization. Ab initio M S calculations of XANES are presented using a code FEFF6X, that includ es estimates of the amplitude reduction factor S-0(2). White-lines and continuum shape resonances in XANES are described quantitatively. We have observed that the atomic background absorption contains oscillato ry structure which can play an important role in XANES. Calculations a nd measurements confirm the existence of AXAFS and show that it can do minate contributions such as multi-electron excitations.