Effects of channel interaction, exchange, and relaxation on the angular distribution and spin polarization of Auger electrons from noble-gas atoms

The angular anisotropy ${\mathrm{\alpha }}_2$ and spin polarization ${\xi }_2$ parameters have been calculated for Ar ${\mathit{L}}_3$MM, Kr ${\mathit{M}}_{4,5}$NN, Xe ${\mathit{N}}_{4,5}$OO, and Xe ${\mathit{M}}_{4,5}$NN Auger transitions using the multichannel multiconfiguration Dirac-Fock method (MMCDF). The results of our MMCDF calculations are in good general agreement with experiment. We have also determined the separate contributions of the exchange, relaxation, and channel interaction to the angular anisotropy of the Auger process. We have shown that especially for Auger lines having at least two strong partial amplitudes corresponding to different values of the orbital angular momentum both the exchange and channel interaction can change the value of the ${\mathrm{\alpha }}_2$ parameter significantly and sometimes even change its sign. Because of the additional eigenchannel phase shifts the ${\mathrm{\alpha }}_2$ parameters are more sensitive to channel interaction than to the exchange. In contrast the relaxation has a small effect on the angular distribution of Auger electrons. A comparative study showed that the ${\mathrm{\alpha }}_2$ parameters are usually less sensitive to correlation than the branching ratios or even the total Auger rates. This was traced back to universal scaling of the modulus of transition amplitudes and to the existence of one dominating ionization channel in most transitions. The ${\xi }_2$ parameters were small for all strong Auger lines and exceedingly sensitive to all correlation effects.