Nondipole parameters in angular distributions of electrons in photoionization of noble-gas atoms

The parameters that determine the nondipole (E1-E2) corrections to the photoelectron angular distribution have been investigated for the s- and p-subshells of the noble-gas atoms through comparing results calculated in the Hartree-Fock (HF) approximation and taking into account multielectron correlations, using the random-phase approximation with exchange. Our results cover the photoelectron energy range ε from the photoionization thresholds to 1.6 keV. We find the interesting result that near the photoionization thresholds these parameters are generally characterized by an oscillatory behavior as a function of ε, exclusive of the parameter for the He $1s$ subshell. These oscillations are sensitive to multielectron correlations, except those of the Ar $3p$ subshell. This finding supports once more that the photoprocesses in these atomic subshells are of a collective character. We conclude that their correct description cannot be achieved within the framework of a one-electron approximation such as the HF approximation. Results are presented and discussed.