PHOTOELECTRON-DIFFRACTION EFFECTS AND CIRCULAR-DICHROISM IN CORE-LEVEL PHOTOEMISSION

We have calculated the circular dichroism associated with core-level p hotoemission using multiple-scattering photoelectron-diffraction theor y. For C Is emission in a chiral geometry from CO adsorbed on Pd(111), photoelectron-diffraction calculations predict the dichroism found in experimental results due to Bansmann et al. and also agree well with prior free-molecule calculations by McKoy and Stephens. Backscattering from the Pd substrate is also found to alter the dichroic asymmetries for different adsorption geometries. Analogous calculations for Fe 2p emission from a small Fe cluster also indicate that dichroism due to a chiral geometry can strongly affect measurements of magnetic circula r dichroism in systems with net magnetization. With generalization to include spin-orbit and multiplet splittings in the initial state and s pin-dependent scattering of the outgoing electrons, photoelectron-diff raction theory thus should provide a general method for modeling disch roism in core-level photoemission from both nonmagnetic and magnetic s ystems.