Double photoionization of excited He-like atoms

We have developed a B-spline based technique for evaluating double photoionization rates for He-like atomic systems. The accuracy of the approach is tested by comparing the results from this code with available theoretical and experimental results for double ionization of the 1s² and 1s2s ¹S states of He. We require significantly more angular momenta to obtain converged results for 1s2s ¹S than for 1s², which is ascribed to the larger spatial extent of the 1s2s ¹S wavefunction. By extending the calculations to Li⁺, Be²⁺, C⁴⁺ and O⁶⁺, we show that no obvious 1/Z² scaling law applies to the ratio between double and single photoionization of the 1s2s ¹S state, in contrast to the 1s^{2 1}S state.