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

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

Kinematically complete experimental study of Compton scattering at helium atoms near the ionization threshold

Compton scattering is one of the fundamental interaction processes of light with matter. Already upon its discovery [1] it was described as a billiard-type collision of a photon kicking a quasi-free electron. With decreasing photon energy, the maximum possible momentum transfer becomes so small that the corresponding energy falls below the binding energy of the electron. Then ionization by Compton scattering becomes an intriguing quantum phenomenon. Here we report a kinematically complete experiment on Compton scattering at helium atoms below that threshold. We determine the momentum correlations of the electron, the recoiling ion, and the scattered photon in a coincidence experiment finding that electrons are not only emitted in the direction of the momentum transfer, but that there is a second peak of ejection to the backward direction. This finding links Compton scattering to processes as ionization by ultrashort optical pulses [2], electron impact ionization [3,4], ion impact ionization [5,6], and neutron scattering [7] where similar momentum patterns occur.Comment: 7 pages, 4 figure

Comment on “Experimental and theoretical study of the triple-differential cross section for electron-impact ionization of thymine molecules”

In their recent paper, Bellm et al. [Phys. Rev. A 85, 022710 (2012)] performed (e,2e) experiments on thymine at an incident energy of 250 eV. They wrote in the conclusion that a model based on the first Born approximation using the completely neglected differential overlap description is in very good agreement with the experimental data. On the contrary, we argue that this model fails to describe experiments on water performed at the same incident energy and is unable to explain any shift of the binary or recoil peaks

Ion and Electron Momentum Distributions from Single and Double Ionization of Helium Induced by Compton Scattering

We present the momentum distributions of the nucleus and of the electrons from double ionization of the helium atom by Compton scattering of photons with hν=40  keV. We find that the doubly charged ion momentum distribution is very close to the Compton profile of the nucleus in the ground state of the helium atom, and the momentum distribution of the singly charged ion to give a precise image of the electron Compton profile. To reproduce these results, nonrelativistic calculations require the use of highly correlated initial- and final-state wave functions

Analytical Representation of Total Cross-Sections for Electron Atom Scattering: Application to Atomic Helium

Based on the series expansion formalism, an analytical approach is proposed to evaluate the total cross-sections induced by electron impact excitation. As an illustration, an analytical expression of the total cross-section of the double excitation of helium atom by electron impact is obtained for the 2p$\text{}^{2}$ $\text{}^{3}$P and 2p3p $\text{}^{1}$P transitions within the framework of the distorted wave Born approximation. The available experimental data are well reproduced by the obtained expression of the total cross-section which is function of the only parameter of the incident electron energy. Comparisons are also made with numerical calculations

Analytical Representation of Total Cross-Sections for Electron Atom Scattering: Application to Atomic Helium

Based on the series expansion formalism, an analytical approach is proposed to evaluate the total cross-sections induced by electron impact excitation. As an illustration, an analytical expression of the total cross-section of the double excitation of helium atom by electron impact is obtained for the 2p$\text{}^{2}$ $\text{}^{3}$P and 2p3p $\text{}^{1}$P transitions within the framework of the distorted wave Born approximation. The available experimental data are well reproduced by the obtained expression of the total cross-section which is function of the only parameter of the incident electron energy. Comparisons are also made with numerical calculations