Nondipole effects in photoemission angular distribution excited by high-energy X-rays

Angular distribution of emitted photoelectrons is theoretically studied for high-energy X-rays where electric quadrupole and magnetic dipole transitions play some important roles in addition to the electric dipole transitions. We apply irreducible tensor expansion of photon field to discuss the high-energy photoelectron angular distribution instead of the usual power series expansion. The present numerical calculations show that the conventional power series expansion works so well up to quite high energy (≈10 keV) for core excitation. Photoelectron diffraction effects make the nondipole contribution sensitive to the geometrical setup of surrounding scattering atoms because of the strong focusing effect in the high-energy region. Total high-energy photoemission intensities from extended levels are well described by use of the Gelius formula because the interference terms are effectively smeared out by Debye-Waller factors.