THEORY OF NATURAL CIRCULAR-DICHROISM IN X-RAY RAMAN-SCATTERING FROM MOLECULES

A theory for natural circular dichroism (CD) in x-ray Raman scattering from molecules is presented. Analytical formulas are given for the CD effect and for the angular dependence of this effect in the electric dipole and in the electric- and magnetic-dipole approximations. It is demonstrated that the CD effect can be observed for randomly oriented molecules even assuming the pure electric-dipole approximation. The ef fect can only be described by a one-step model for x-ray Raman scatter ing, while in the two-step model the electric CD contribution is ident ically zero. The effect is intimately connected to the molecular point -group symmetry and to channel interference, and, contrary to optical CD, it will preferentially be observed for ''achiral'' molecules. It i s shown that it acts as a unique experimental tool to identify the deg ree of dynamic localization of core excited states. Sample calculation s indicate that the electric contribution to the molecular CD effect c an be very large and about one order of magnitude lar er than the magn etic-dipole contributions.