DOUBLE PHOTOIONIZATION OF HELIUM AT LOW PHOTON ENERGIES

The cross sections for single and double photoionization of helium at energies from the threshold of double ionization to 280 eV are calcula ted by combining the previously developed hyperspherical close-couplin g method with a discretization procedure for the continuum spectrum of He+. No pseudoresonances due to the discretization are found. Both th e length and acceleration forms of the dipole operator are used, and t he results hardly depend on these different gauges. The results are co mpared with previous theories and experiments.