Double-photoionization calculations of the helium metastable 2 S-1,S-3 states - art. no. 052724

Theoretical results are presented for double photoionization and ionization with excitation of the metastable 2 S-1,S-3 states of helium. We employ th e momentum space formulation of the close-coupling theory to describe nonpe rturbatively the electron-electron interaction in the final state. A large Laguerre basis is used to obtain convergent close-coupling (CCC) results. I n addition, we employ a B-spline basis for the target states. The presented results cover continuously the photon energy range from the double-photoio nization threshold to the asymptotic limit of infinite photon energy. Near the threshold our data generally support the calculations of van der Hart e t al. [Phys. Rev. A 57, 3641 (1998)]. At large photon energies our results merge continuously with the asymptotic values derived from the metastable s tate 2 S-1,S-3 wave functions. Proportionality between the double-to-single photoionization cross-sections ratio and the cross section of electron-imp act ionization of the ion is tested to examine the relative contributions o f different mechanisms of the two-electron photoionization in the ground an d metastable states of the helium atom.