https://doi.org/10.1140/epjd/s10053-025-01005-x
Regular Article – Atomic and Molecular Collisions
Single ionization of helium by 75 keV protons outside the velocity-matching regime in the parabolic quasi-Sturmian approach
1
School of Fundamental and Computer Sciences, Pacific National University, 680035, Khabarovsk, Russia
2
Université de Lorraine, CNRS, LPCT, 57000, Metz, France
3
Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119991, Moscow, Russia
4
Bogoliubov Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, 141980, Dubna, Moscow region, Russia
5
Department of Nuclear Physics and Quantum Theory of Collisions, Faculty of Physics, Lomonosov Moscow State University, 119991, Moscow, Russia
Received:
18
February
2025
Accepted:
24
April
2025
Published online:
21
May
2025
The parabolic quasi-Sturmian approach is applied here to 75 keV 
ionization process. We calculate fully differential cross sections (FDCS) for electrons ejected into the scattering plane with energies far from the velocity-matching case. Our results provide the first comparison, on a variety of kinematical and geometrical configurations, with recent experimental absolute scale data. To obtain the ionization amplitude in such an energy regime, we use convolutions of two quasi-Sturmian functions (CQS) that satisfy the so-called 2C-like model, within which the proton-ion and electron-ion interactions are taken into account exactly. In turn, the proton-electron interaction is taken into account by means of an equation of the Lippmann-Schwinger type that is solved using an expansion of the potential in Sturmian functions. To improve the rate of convergence as more terms are included in the potential separable representations, it appears necessary to use smoothing factors in combination with an optimal choice of the basis scaling parameter. As far as the binary peak position is concerned, the calculated FDCSs are found to be in reasonable agreement with recent experimental data; the magnitude agreement goes from bad to good according to the considered configuration. In contrast to the experimental statement that non-postcollision interaction effects are dominant at small energy losses, we do not reach the same conclusion. Although the considered kinematics are far from the velocity-matching regime, the role played by electron capture may be responsible for some experimentally observed features that clearly do not appear in our theoretical description.
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Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
