Angular distributions for double photoionization of helium: Discrepancies between theory and experiment

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Abstract
We apply two different methods to the calculation of the triply differential cross section (TDCS) for double ionization of helium. In one method, the 3C method, the final state is described by a product of 3 Coulomb continuum wave functions, while in the other method, the 2SC method, the final state is described by a product of 2 screened Coulomb wave functions employing effective charges. We present results at the energies and geometries covered in the recent experiment by Lablanquie et al. [Phys. Rev. Lett. 74, 2192 (1995)]. There are substantial discrepancies. We also comment on a recent measurement of the absolute TDCS by Schwarzkopf and Schmidt [J. Phys. B 28, 2847 (1995)]. The measured result, as originally reported, is a factor of two smaller than the value for the absolute TDCS calculated using the 2SC method. We discuss this discrepancy. © 1996 The American Physical Society.