ANGULAR-DISTRIBUTIONS FOR DOUBLE PHOTOIONIZATION OF HELIUM - DISCREPANCIES BETWEEN THEORY AND EXPERIMENT

We apply two different methods to the calculation of the triply differ ential cross section (TDCS) for double ionization of helium. In one me thod, the 3C method, the final state is described by a product of 3 Co ulomb continuum wave functions, while in the other method, the 2SC met hod, the final state is described by a product of 2 screened Coulomb w ave functions employing effective charges. We present results at the e nergies and geometries covered in the recent experiment by Lablanquie et al. [Phys. Rev. Lett. 74, 2192 (1995)]. There are substantial discr epancies. 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 v alue for the absolute TDCS calculated using the 2SC method. We discuss this discrepancy.