Theory of X-ray natural circular dichroism

A theoretical approach is presented to calculate the natural circular dichr oism recently discovered in the x-ray range (XNCD). XNCD is shown to be due to an interference of electric dipole and quadrupole transitions. The basi c formula represents XNCD as an odd second-rank tensor. The crystal symmetr ies compatible with XNCD are determined. Sum rules are derived that relate XNCD to the mixing of odd and even orbitals on the absorbing site in the gr ound state. A multiple-scattering theory of XNCD is presented. The results are analyzed to show that XNCD is sensitive to the relative orientation of the cluster shells. A scattering path analysis is carried out to identify t he paths responsible for the signal.