Photoelectron angular distributions beyond the dipole approximation

This paper reports the measurement of nondipolar asymmetry parameters for the angular distributions of Ar 1s, Kr 2s, and Kr 2p photoemission within 2-3 keV above their respective thresholds. Pronounced asymmetries with respect to direction of photon propagation are present even at low electron kinetic energies. The energy dependence of the asymmetry is Z- and subshell-specific and causes the direction of preferred electron emission to change sign at least once in each case. Towards higher energies, the asymmetry increases and the photoelectron emission pattern is forward-skewed for all 3 cases. Measured asymmetry parameters are in good agreement with recent predictions from nonrelativistic calculations which include interference between electric-dipole and electric-quadrupole transition amplitudes in the photoabsorption process