Large nondipole correlation effects near atomic photoionization thresholds

The parameter that determines the nondipole correction to the angular distr ibution is calculated for Ar is and 3s subshells in the Hartree-Fock (HF) a pproximation and taking account of the multielectron correlations, using th e random-phase approximation with exchange. In the photoelectron energy ran ge 0-100 eV the parameter, which for s subshells is nonzero at threshold, i s found for Ar 3s to be strongly affected by multielectron correlations. Re sults are also presented for He and Be in the HF approximation. [S1050-2947 (99)50804-4].