Experimental determination of nondipolar angular distribution parameters for photoionization in the Ar K and Kr L shells

We report the measurement of nondipolar asymmetry parameters for the angular distributions of argon 1s, krypton 2s, and krypton 2p photoemission within 2-3 keV above their respective thresholds. Pronounced asymmetries with respect to the 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 of the cases studied. Towards higher energies the asymmetry increases and the photoelectron emission pattern is forward skewed for all three cases. The measured asymmetry parameters are in good agreement with recent predictions from nonrelativistic calculations which include the interference between electric-dipole and electric-quadrupole transition amplitudes in the photoabsorption process.