PUB - Publikationen an der Universität Bielefeld

Resonances in quadrupole channels corresponding to the np --> epsilonf transitions are investigated in atoms preceding Ce (Z = 59) and Pa (Z = 91), where the 4f and 5f shells, respectively, start to be filled. These resonances lead to a prominent enhancement of all non-dipole effects in the angular distribution and spin polarization of photoelectrons at low photon energies of the order of 100-200 eV. Since in atoms between Cd and Xe the 4p(1/2) photoline is absent from the photoelectron spectrum, we investigate these effects in more detail in Hg where both 5p(1/2) and 5p(3/2) lines are present. We demonstrate that near these resonances the non-dipole contribution to the degree of polarization of photoelectrons in Hg can be of the order of 5%. For the absorption of linearly polarized light the degree of polarization due to the non-dipole contribution tends towards 100%, but the photoelectron intensity in that case tends towards zero. Corrections to the photoelectron intensities in the angular distributions at some angles can exceed 10%. The similar resonance effects in Rn are expected to be substantially stronger.