Positron-lithium-atom collisions using the two-state approximation

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Abstract
The two-state approximation is applied to positron-lithium-atom collisions considering only the elastic scattering and the ground-state positronium formation. Taking the effect of the adiabatic polarization potential into account in both the direct and rearrangement channels, results for the differential, total, and momentum-transfer cross sections are computed at incident positron energies 0.5-10 eV. While for the elastic scattering the present data show satisfactory agreement with other available calculations, for positronium formation the present results are quite new and give us an idea of the order of the cross section. It is found that the differential cross section for both the elastic scattering and positronium formation shows a deep minimum at low energies of positron impact in agreement with available earlier findings.