Photoionization of metastable state 1s2s 1S0 of helium

The interference effects between the direct and indirect photo ionization processes from the metastable state 1s2s S-1(0) of helium arc studied by employing the multi-configuration Dirac-hock (MCDh) method combining with the Fano parameterization technique. Good agreement is found between the present calculations and the available experimental results. It is shown that the interference effects, which further modified the direct photoionization cross sections even far away from the resonances, play an important role in reproducing the resultant nonresonant background beside the configuration interaction in bound ionic states.