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A single-center coupled pseudostate approximation originally used by McGovern et al. [Phys. Rev. A 79, 042707 (2009)] to study differential ionization under ion impact is extended to take account of electron exchange. The approximation is fully quantal and includes the interaction between the projectile and target nuclei as well as post-collisional interactions between the ionized electron and the two nuclei. Calculations are presented for proton-impact ionization of atomic hydrogen at 75 keV. These include fully (triple) differential cross sections which illustrate how the post-collisional interaction switches from being dominated by the interaction between the ejected electron and the target nucleus to being dominated by the electron interaction with the projectile nucleus (charge exchange to the continuum). Comparison is made with some measurements of the double differential cross section with respect to ejected electron energy and proton scattering angle. While overall agreement between theory and the experimental data is encouraging, detailed agreement is lacking. The need for more experimental work is emphasized. [ABSTRACT FROM AUTHOR]

The coupled pseudostate approximation (CP) introduced by McGovern et al. [Phys. Rev. A 79,042707 (2009)] to study differential ionization in heavy particle collisions is extended to the case of a Li target. Symmetry properties dependent upon the initial state of the target, and the role of the interaction between the projectile and target nuclei, are discussed. Comparison is made with the recent double differential cross-section measurements (d²σ/dEdq,) of LaForge et al. [J. Phys. B 46, 031001 (2013)] for proton impact at 6 MeV and 08+ impact at 1.5 MeV/amu on Li(2i) and Li(2p). It is shown that the proton measurements lie very much in the first Born regime and that the comparison is therefore more of a test of the experiment than of the theory which, at the first Born level, is considered to be quite accurate. By contrast, the 08+ ' measurements present a nonperturbative scenario which provides a substantive challenge to the full CP theory. Although there are exceptions, the CP approximation generally agrees well with the shape of the 08+ data but there is a drift in normalization between the calculated and measured cross sections with increasing electron ejection energy. This same drift is seen in comparison between CP and measurements of da/dE from Fischer et al. [Phys. Rev. Lett. 109, 113202 (2012)]. The convergence of the CP approximation with respect to the angular momenta of the pseudostates and their number is investigated. It is concluded that the 164-state set employed here should be satisfactory. Comparison is also made with the even more recent fully differential (triple differential) measurements of Hubele et al. [Phys. Rev. Lett. 110, 133201 (2013)] for 08+ impact on Li(2s) and Li(2p) at 1.5 MeV/amu. The CP approximation reproduces the "wings" seen in the Li(2s) measurements, which are due to the interaction between the projectile and target nuclei and the node in the 2s wave function, and the asymmetric shape of the 2p data. The orientational dichroism between the 2p+1 and 2p-1states is illustrated. Overall, and while not perfect, the agreement between the pseudstate theory and the experiments is very encouraging. [ABSTRACT FROM AUTHOR]

A recent theoretical paper [Colgan et al, J. Phys. B 44, 175205 (2011)] has reopened the problem of C6+ ionization of He at 100 MeV/amu. The issue concerns ionization in the plane perpendicular to the momentum transfer q for the case where the ejected electron has an energy of 6.5 eV and q = 0.75 a.u. Here, even after deconvolution, experiment finds two peaks near 90° and 270°, contrary to earlier theoretical works that had predicted dips. Now, Colgan et al. also find peaks. We have reinvestigated the problem using the second Born approximation whose results are supported by a nonperturbative impact-parameter coupled-pseudostate approximation. Dips are again predicted. By comparing C6+ impact with that of its antiparticle C–- a "mirror-image" situation is observed in which the dips are converted into peaks, i.e., positively (negatively) charged projectiles give dips (peaks) near 90° and 270°. A physical interpretation of this result is suggested. Applying exactly the same second Born approximation to e± impact ionization of He at 1 keV under similar dynamical conditions to C6+, we see exactly the same patterns, but now the results for e-, showing peaks near 90° and 270° in the plane perpendicular to q, are in quite good agreement with experiment in this and other geometries. This is strong support for the predictions of the second Born approximation for C6+. A paper by Egodapitiya et al. [Phys. Rev. Lett. 106, 153202 (2011)] warns of coherence problems with heavy-particle beams. It is suggested that this, together with experimental resolutions, may explain the experimental data for C6+. [ABSTRACT FROM AUTHOR]

We report calculations of differential and integral cross sections for positron scattering by noble gas and alkaline-earth atoms within the same methodology. The scattering potentials are constructed by scaling adiabatic potentials so that their minima coincide with the covalent radii of the target atoms. Elastic differential and integral cross sections are calculated for Ne, Ar, Be, and Mg, and the results are very close to experimental and best theoretical data. Particularly, elastic differential cross sections for Be and Mg at low energies are reported. [ABSTRACT FROM AUTHOR]