Scaling laws in double photoionization

Double-photoionization cross sections are calculated for two-electron targets H-, He, Li+, and O6+ using a correlated and an uncorrelated two-electron continuum wave function (C3 and C2 models, respectively). As the target nuclear charge ZT is increased, the double-photoionization cross section is found to scale as ZT-4 and the electron energy distribution as ZT-6. Conclusions are extracted about the behavior of the cross sections in the high-energy and threshold regions. The ratio of double to single photoionization scales as ZT-2, as in the case of proton impact