The eigenchannel R-matrix method for single photoionization is extended to describe a class of two-electron escape processes. We apply this approach to calculate the double photoionization of helium by single-photon absorption for photon energies in the range 80–280 eV. Pseudoresonances in the double continuum are eliminated by performing a Gailitis average and by averaging the final spectrum over the size of the R-matrix box. Calculations are presented in both the velocity and acceleration gauges. The ratio of double- and single-photoionization cross sections, a key parameter for characterizing electron correlations, is compared to existing theoretical and experimental values.

DOI:https://doi.org/10.1103/PhysRevA.50.R3573