Angular distribution of ejected electrons from autoionizing 3pns states of magnesium

We have measured the angular distribution of electrons ejected from doubly excited autoionizing Rydberg 3pns J=1 states of magnesium, where n=10--20. Two dye lasers cross an atomic beam and excite 3sns1S0 states of Mg. A third linearly polarized laser excites the 3pns states. The angular distribution is of the form (σ/4π)[1+βP2(cosθ)]. We measure β as a function of the energy of the third laser. The β parameter varies over its full range of values, -1 to 2. Our data agree quite well with the predictions of the reaction-matrix--multichannel-quantum-defect theory