Ionization of Helium by Proton Impact in a Quasi-Sturmian Approach Built upon the 3C Model

We investigate theoretically the 75 keV proton-impact ionization of atomic helium. The convoluted quasi-Sturmian approach is extended to treat, on an equal footing, both the direct mechanism and the electron capture to the continuum. This is achieved by proposing an ansatz of the Green’s function of the three-body Coulomb system (e−,He+,p+) that is compatible with the well-known 3C correlated continuum wave function. The model that stems from this approximation, named 3C˜, is tested numerically using parabolic Sturmian expansions. Calculations of fully differential cross sections are presented for different regimes of energy losses, namely for ejected electron energies below, nearly equal to, and above the cusp energy. Our results are compared with recent experimental measurements and other theoretical calculations. The proposed 3C˜ model yields very encouraging results and paves the way towards a more advanced Lippmann–Schwinger approach based on the 3C model.