High-energy two-electron photoabsorption as a three-body problem

We study the high-energy behaviour of double photoionization and of the ionization accompanied by excitation of the states n¹S and n ³S of the H^-ion, helium atom, and light helium-like ions. We show that the high-energy nonrelativistic limit of the "ionization + excitation" to the single-ionization cross section ratio is still valid for the photon energies, corresponding to the relativistic energies of the outgoing electron. The same applies to the double photoionization of the triplet states. The situation for the double photoionization of singlet states differs due to the quasifree mechanism. All these ionization ratios are calculated by using the high-precision locally correct wave functions for the bound electrons. The importance of using locally correct functions is emphasized.