Role of the ground state in electron-atom double ionization.
Recently, absolute measurements have been reported for double ionization of helium by 5.6 keV electron-impact. At this high energy, one would think that the first Born approximation for the interaction of the projectile with the atom would be valid. However, on the basis of a lowest-order implementation of a Faddeev-type approach, Berakdar [Phys. Rev. Lett. 85, 4036 (2000)]] concluded that the approximation was not valid. Here we argue that (i) it is valid at this energy and (ii) the previous discrepancy between calculations in the first Born approximation and the overall magnitude of the measurements was due to a poor description of the ground state.
Jones
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Laboratory for Atomic, Molecular and Optical Research, Physics Department, University of Missouri-Rolla, Rolla, MO 65409-0640, USA.
Madison
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