Complementary TDCS for the photo-double ionization of He at 40 eV above the threshold in unequal energy-sharing conditions

Photo-double ionization (PDI) of helium at 40 eV above the threshold has been studied for unequal energy-sharing in the complementary kinematics obtained in two measurements by the interchange of the kinetic energies E-1 <----> E-2 of the two photoelectrons. The triple differential cross sections (TDCS) were measured in the plane perpendicular to the photon direction using the multicoincidence end-station of the gas-phase photoemission beam-line of the Elettra storage ring. The measured TDCSs were compared with previous experimental results using a practical parametrization proposed by Cvejanovic and Reddish (2000 J. Phys. B: At. Mol. Opt. Phys. 33 4691) and with predictions of the 3C and convergent close-coupling calculations. Satisfactory agreement with the previous experimental data was found. The comparison with the two theoretical models shows that the TDCSs in the complementary kinematics still present a challenge for PDI theory.