Calculation of helium photoionization with excitation including angular distribution and resonance structure

A nine-channel coupled-equation calculation for photoionization of the 1s² ground state of He is performed within the framework of many-body perturbation theory. Partial cross sections for leaving the ion in 1s, 2s, 2p, 3s, 3p, and 3d levels are obtained together with the angular asymmetry parameter for leaving the ion in n=2 states. The resonance structure in the 1s, 2s, and 2p cross sections and in the n=2 angular asymmetry parameter due to doubly excited autoionizing states below the n=3 threshold is calculated. Also, parameters describing the resonances in the 1s cross section below the n=2 threshold are obtained.