Non-dipole effects in photoelectron angular distributions for rare gas atoms

We present a theoretical study of O(ka) and O(k(2)a(2)) corrections to the dipole approximation in photoionization of rare gas atoms, where k is the magnitude of the photon wave vector and a is the radius of the ionized subshell. In the dipole approximation, the photoelectron angular distribution is characterized by the single parameter beta. The O(ka) corrections are characterized by two parameters gamma and delta, and the O(k(2)a(2)) corrections are characterized by three parameters lambda, mu, and nu, constrained by the relation lambda + mu + nu = 0 and a correction Delta beta to the dipole parameter beta. Formulas are given for the non-dipole parameters in terms of reduced matrix elements of electric and magnetic multipole operators. Tables and graphs of the seven angular distribution parameters, calculated in the relativistic independent-particle approximation (IPA), are given for electron energies ranging from 20 to 5000 eV for all 41 subshells of the rare gas atoms He, Ne, Ar, Kr, and Xe. Tables and graphs of the O(ka) parameters are also given in the energy range 2-60 eV for the n = 3 and 4 shells of Kr, and for the n = 4 and 5 shells of Xe, where interesting non-dipole effects are found. Comparisons of the IPA calculations with correlated relativistic random-phase approximation calculations are made for selected subshells of Ar and Kr, illustrating the influence of correlation on the non-dipole parameters. (C) 1999 Academic Press.