Accurate spectral approach for the calculation of doubly excited 1Po states of Li+

We report in this paper computed resonant parameters for the lowest singlet doubly excited 1Po states of the Li+ ion lying below the N=2 and N=3 hydrogenic thresholds. In our previous works (see Barmaki et al., 2014 and references therein), the calculation of the energy spectrum of a two-electron system was performed with a spectral method of configuration-interaction type that consists in expanding the radial part of the two-electron wave function on antisymmetrized products of B-spline functions. We combine in this paper the expansion of the wave function on B-spline functions with the complex rotation method in order to have access to the spectral data of the 1Po resonances embedded between the Li2+(Nℓ) thresholds. The present approach has the advantage to generate the energy positions and the widths of the resonances in a single calculation. The obtained results are in very good agreement with other available experimental and theoretical data.