Two-dimensional electron-momentum distributions for transfer ionization in fast proton-helium collisions

Abstract

The momentum distribution of the electron in the reaction p+He → H + He 2+ + e is measured for projectile energies E p =300 and 630 keV/u at very small scattering angles of hydrogen. We mainly present two dimensional distributions parallel (k || ) and perpendicular (k ⊥ ) to the projectile beam. Theoretical calculations were carried out within the Plane Wave First Born Approximation (PWFBA), which includes both electron emission mechanisms, shake-off and sequential capture and ionization. It is shown that electron correlations in the target wave function play the most important role in the explanation of experimentally observed backward emission. Second order effects have to be involved to correctly describe the forward emission of the electron. * Electronic address: schoeffler@atom.uni-frankfurt.de 2

Transfer excitation reactions in fast proton-helium collisions

“…The symbol < ϕ − ( k)|T > denotes the transfer ionization amplitude, where the emitted electron is described by a Coulomb wave [13,14]; < k|T > is the same, but the Coulomb wave is replaced by the plane wave. Here we have 6D and 7D integrals.…”

“…Transfer ionization, where one electron is captured into a bound state of the projectile and a second one is released into the continuum, have been studied in great detail [2][3][4][5][6][7][8][9][10][11][12][13][14] and have led to a better understanding of initial and final state correlation [15][16][17]. Instead of being lifted to the continuum, the second target electron can also be promoted to a bound but excited state.…”

Time-dependent calculations of transfer ionization by fast proton-helium collision in one-dimensional kinematics

“…However, the plane wave first Born approximation (PWFBA) [9] strongly overestimates forward emission. This implies that the deviations of the PWFBA calculations from the experiment [4,5] may be attributed to the shortcomings of this specific implementation rather than contribution from the further Born terms.…”

“…This potential was further explored in [2,3]. Later on, the experimental set up was improved to detect the complete three-particle coincidence H− He 2+ − e − and to map three-dimensional ejected electron momentum distributions [4][5][6]. On the theoretical side, various calculations were performed employing the lowest order perturbation theory in the form of the Born series.…”

“…A more detailed comparison with experimental data, in the form of the fully differential cross sections, was not possible at the time. Indeed, in the earlier experiments [1,2], the momentum distribution of the ionized electron was derived from the momentum and energy conservation with other collision partners, but not directly measured as in the latest experiments [4,5]. Nevertheless, the authors of Ref.…”