Angle resolved photoemission from adsorbates: Theoretical considerations of polarization effects and symmetry

Angular distributions of photoemission from chemisorption induced states and LEED spectra are calculated for the p(2 × 2) and the c(2 × 2) oxygen superstructure on the (001) surface of nickel. The obtained dependence of the photoemission intensity on the polar angle, on the azimuth angle of emission and on the direction of the light beam is discussed using mainly symmetry arguments (selection rules). This kind of analysis is shown to be useful for identifying the orbital symmetry or the symmetry of the adsorbate position without carrying out complicated calculations.