Multipole effects in the angular distribution of photoelectrons

The influence of contributions corresponding to different multipoles L of a radiation field on the angular distribution of photoelectrons upon photoio nization of an atom is considered for linearly polarized photons. Relativis tic calculations of the differential photoionization cross section are carr ied out taking into account all multipoles, whose contributions are appreci able, for all shells of atoms with Z = 10, 30, 54, 80, and 94 in the region of photoelectron kinetic energies 0.5 keV less than or equal to E-k less t han or equal to 500 keV. The self-consistent Dirac-Fock-Slater potential is used. The calculated results showed that for photoelectron energies E-k le ss than or similar to 5 keV, the angular distribution is, on the average, w ell described in the quadrupole approximation (L less than or equal to 2). However, the quadrupole approximation is insufficient for the adequate desc ription of the experimentally measured nondipole parameter. in this case, t he next, octupole approximation (L = 3) contributes significantly. For ener gies Ek; : 5 keV, it is necessary to consider higher multipoles (up to L ap proximate to 50 at E-k = 500 keV). As the energy increases, the angular dis tribution of photoelectrons becomes increasingly asymmetric and is shifted toward smaller angles. (C) 2001 MAIK "Nauka/Inteiperiodica".