Comment on "Four-body charge transfer processes in proton--helium collisions"

We found, within the plane-wave first Born approximation (PWFBA), that the proton-helium fully differential cross section (FDCS) for transfer excitation agrees well with the experimental one at the proton energy Ep = 300 keV and small scattering angles both in shape and in magnitude. This result is in a contradiction with that obtained in [1].Comment: 4 pages, 2 figure

Photon Momentum Transfer in Single-Photon Double Ionization of Helium

We theoretically and experimentally investigate the photon momentum transfer in single-photon double ionization of helium at various large photon energies. We find that the forward shifts of the momenta along the light propagation of the two photoelectrons are roughly proportional to their fraction of the excess energy. The mean value of the forward momentum is about 8/5 of the electron energy divided by the speed of light. This holds for fast and slow electrons despite the fact that the energy sharing is highly asymmetric and the slow electron is known to be ejected by secondary processes of shake off and knockout rather than directly taking its energy from the photon. The biggest deviations from this rule are found for the region of equal energy sharing where the quasifree mechanism dominates double ionization

Transfer ionization and its sensitivity to the ground-state wave function

We present kinematically complete theoretical calculations and experiments for transfer ionization in H$^++$He collisions at 630 keV/u. Experiment and theory are compared on the most detailed level of fully differential cross sections in the momentum space. This allows us to unambiguously identify contributions from the shake-off and two-step-2 mechanisms of the reaction. It is shown that the simultaneous electron transfer and ionization is highly sensitive to the quality of a trial initial-state wave function

Single photon double ionization of Helium at 800 eV - observation of the Quasi Free Mechanism

In a kinematically complete experiment we have measured the photo double ionization of Helium at aphoton energy of 800 eV and observed He2+ ions with 0 momentum, corresponding to a back-to-back-emissionof the two electrons. The results are in good agreement with theoretical calculations