Polarization effect on He doubly excited states below the N=2 threshold of He⁺

Based on the R-matrix method, photoionization cross sections of He below the N=2 threshold of He⁺ are calculated, and a definite assignment of the doubly excited resonance states is determined by the eigenchannel treatment. Our results are in good agreement with the experimental data and other theoretical works. The polarization effects on the doubly excited states are studied in detail. We elucidate the effects of the dynamic polarization within the reaction zone (i.e., R-matrix box) and the long-range static polarization potentials outside the reaction zone, which influence the resonance energies and the profiles of He resonance states.