Non-dipole effects in X-ray standing wave photoelectron spectroscopy experiments

The influence of different multipole terms to the angular resolved photoelectron yield excited by an X-ray standing wave (XSW) field which is generated by two coherent waves is discussed. The contributions of dipole and quadrupole terms are analyzed for a distribution of atoms within the interference field. General expression for the photoelectron yield in the XSW field is discussed in details. It is shown how non-dipole contributions can be obtained experimentally. A comparison between theoretical and experimental results is presented.