Double-excited resonant structure of photoionization

The dominant diagrams were found in double-excited resonant structure of photoionization by using many-body perturbation theory. Based on the characteristics of these diagrams, the couple-equation method was improved, and the summation of specific classes of these diagrams is to an infinite order, and the resonant peaks with the widths are obtained first. The doubled-excited resonant structures (2p, 3s)-->(3p, np), (3p, nf), (3d, nd), (3d, ns) and (4s, ns) of the photoionization processes 2p-->ks, kd are obtained. The photoionization with excitation process (2p; 3s)-->(3p, kp) was included in the calculations. The results of calculations are compared with the experimental data from 38.5 to 46.8 eV photon energies, which are in good agreement with the experiment.