Abstract
The coupled pseudostate approximation (McGovern et al 2009 Phys. Rev. A 79 042707) has been applied to Li2+ + Li(2s, 2p0,±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 Li2+ is frozen in the 1s state and its screening of the Li2+ nucleus is fully taken into account. Previous calculations on this system (3DW-EIS and CDW-EIS) have treated the Li2+ 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 d2σ/dEdqt and the single differential cross section dσ/dE are also calculated. Here 1s screening is found to be important at large (transverse) momentum transfers qt and large ejection energies E. In addition, the pseudostate approximation gives cross sections for discrete transitions, total ionization and total scattering.
Highlights
Cold target recoil ion momentum spectroscopy (COLTRIMS) [1, 2] has been a highly successful technique for the detailed study of differential ionization of atoms and molecules
Our primary concern in this paper are the triple differential cross sections (TDCS) measurements of Ghanbari-Adivi et al [8]. These have been made for ionization of Li(2s) and Li(2p) for ejection energies of 2, 10 and 20 eV and momentum transfers q of 0.4 au and 1.0 au in each case
Where the agreement is best we find that the cross section is very much first Born, i.e. it is no test of higher order approximations
Summary
Cold target recoil ion momentum spectroscopy (COLTRIMS) [1, 2] has been a highly successful technique for the detailed study of differential ionization of atoms and molecules. The first Born approximation does not take account of the interaction between the projectile and target nuclei (suitably screened by any passive electrons if necessary) (we shall refer to this as the NN interaction) and so we must not expect it to be viable in situations where the NN interaction may be important [9,10,11,12,13,14,15] (usually the larger momentum transfers) For those kinematics which contribute most to the total ionization cross section, η may not be a bad guide. The basis takes account of all important dynamical factors, including those associated with the initial and final state interactions of the projectile with the active electron It gives a description (dependent upon the basis) of all the main physical processes, e.g. elastic scattering, discrete excitations of the target, total ionization; in this sense we get a complete, and internally consistent, picture of the outcomes of the collision (e.g. see table 1 of the present paper). The symbol a0 denotes the Bohr radius and all reported differential cross sections refer to the laboratory frame of reference [9]
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