CONTRIBUTIONS OF MULTIPOLE TERMS TO THE PHOTOELECTRIC YIELD IN X-RAY STANDING-WAVE MEASUREMENTS

The influence of higher-order multipole terms in the photoelectron yie ld on the result of an X-ray Standing Wave (XSW) measurement is discus sed. The contributions of dipole, quadrupole and octupole term are ana lyzed for the simple model of a single atom within the XSW field. It i s shown that each multipole term shows a different dependence on the p olarization Vectors and wavevectors of the direct and diffracted beam. The model is generalized for the case of a monolayer of atoms adsorbe d on the surface of a crystal. We outline how multipole contributions can be determined by an XSW measurement.