Non-dipole effects in spin polarization of photoelectrons from Xe 4p and 5p shells

The contribution of electric-dipole-electric-quadrupole interference terms (the lowest-order non-dipole corrections) to the spin polarization of photo electrons ejected from atomic np-shells is analysed theoretically. The nume rical calculations in the non-relativistic random phase approximation with exchange for Xe 4p and 5p shells show that these corrections even at low ph oton energies (below 350 eV) can be observed, especially in the regions whe re the spin polarization parameters in the electric-dipole approximation ar e approaching zero values. For the 5p shell the contribution of non-dipole terms to the spin polarization of photoelectrons is of the order of a few p er cent, while for the 4p shell it can be as large as 15%. This changes com pletely the shapes of the corresponding angular dependences near the ioniza tion threshold of the 4p shell. Possible experimental geometries are propos ed, which allow an easy observation of these non-dipole effects.