Collision of Li 2+ with Li(2s) and Li(2p): differential and total ionization; discrete excitations; elastic scattering, and total cross section

The coupled pseudostate approximation (McGovern et al 2009 Phys. Rev. A 79 042707) has been applied to Li 2+ + Li(2s, 2p 0,±1 ) collisions at 16 MeV with emphasis on studying the fully differential ionization measurements of Ghanbari-Adivi et al in the azimuthal plane (2017 J. Phys. B: At. Mol. Opt. Phys. 50 215202). The states of the valence electron in the Li target are calculated using the model potential of Stein (1993 J. Phys. B: At. Mol. Opt. Phys. 26 2087). Altogether 164 states with angular momenta l = 0 to 9 are employed in the scattering calculation. It is assumed that the electron in the Li 2+ is frozen in the 1s state and its screening of the Li 2+ nucleus is fully taken into account. Previous calculations on this system (3DW-EIS and CDW-EIS) have treated the Li 2+ as a bare ion with a nuclear charge of 2 au. Except for normalisation, agreement with the experimental data of Ghanbari-Adivi et al is generally quite good. But, where agreement is best it is found that the cross section is very much first Born. Except in one case, quite good accord is also obtained with the 3DW-EIS calculations of Ghanbari-Adivi et al , particularly on normalisation. Screening by the 1s electron has little effect on the fully differential calculations undertaken here. The double differential cross section d 2 σ / dEdq t and the single differential cross section dσ / dE are also calculated. Here 1s screening is found to be important at large (transverse) momentum transfers q t and large ejection energies E . In addition, the pseudostate approximation gives cross sections for discrete transitions, total ionization and total scattering.