Evolution of angular anisotropy of Auger emission across krypton 3d and xenon 4d thresholds

The n dependence of the angular anisotropy parameters of the Kr 3d_5/2^-1np → 4p⁴mp (n, m ≥ 5) and Xe 4d_5/2^-1np ≥ 5p⁴mp (n, m ≥ 6) transitions has been studied by experiment and theory. The spectator-induced mixing of core states strongly affects the anisotropy at first resonances. Hence the fine structure averaged angular distribution of a resonant Auger spectrum differs from that of the corresponding normal Auger spectrum. As the excitation energy is tuned to higher resonances and across the pertinent ionization thresholds, the differences gradually vanish. Because of the spin-orbit splitting, the Kr 3d_5/2^-16p state is nearly degenerate with 3d_3/2^-15p, and the Xe 4d_5/2^-1 np (n = 8-10) states are degenerate with 4d_3/2^-16p. As these states are excited coherently the angular anisotropy coefficients cannot be written in a form describing the excitation and decay processes separately, but rather the one-step characteristics of the transition must be taken into account. The effect of coherence on the angular anisotropy is discussed.