Effect of positive-energy orbitals on the photoionization cross sections and oscillator strengths of He and divalent atoms

The effect of the positive-energy continuum orbitals to the photoionization and bound-bound transitions in He and Mg-like divalent Al⁺ ion is estimated quantitatively in a B-spline-based configuration-interaction calculation. Our calculation has also shown that the theoretical uncertainty in radiative lifetimes measured in terms of the difference between the length and velocity results, due to the use of a parametrized long-range dipole core-polarization potential, is approximately 1--3 % for the Mg-like divalent Al⁺ ion.