INELASTIC COLLISIONS OF POSITRONS WITH BERYLLIUM AND MAGNESIUM IONS

The collision of positrons with beryllium and magnesium positive ions is treated for the first time as a three-channel problem with the assumption that the elastic, ground-positronium and excited-positronium formation channels are open. A one-valence-electron model for the targets, based on the Clementi–Roetti Slater basis functions, as well as an improved coupled-static approach allowing for the polarization of the excited positronium, are used for calculating the partial cross-sections of eight partial waves (corresponding to 0≤ℓ≤7, where ℓ is the total angular momentum of the scattering problem considered). The calculations are carried out, in each case, at 19 values of the incident energy lying above the excited positronium formation threshold (i.e. above 16.42 eV in e +– Be + scattering and above 13.02 eV in e +– Mg + scattering). The total elastic cross-sections of e +– Mg + scattering show a peak around the ionization threshold of Mg + (at 14.723 eV) but for e +– Be + scattering, display a peak at 90 eV (remember that the ionization threshold of Be + is 18.2 eV). Although the resulting total collisional positronium formation cross-sections are smaller than the elastic ones, their relatively large values should draw the attention of experimental and theoretical physicists to the field of positron–ion collisions.