Positronium formation for positron scattering from helium ion

Positronium (Ps) formation processes from helium ions by positron impact are studied using the two-channel two-center eikonal final state–continuum initial distorted wave method. The Ps(n = 1 and 2) and total Ps formation cross sections are calculated from the threshold to the high energy region, and the results are compared with other theoretical calculations available in the literature. It is found that the present results agree reasonably well with the close-coupling calculations, while other predictions, such as the Coulomb–Born approximation, the optical potential method, and the recent classical trajectory Monte Carlo method (Naginey 2014 Phys. Rev. A 89, 062704), are all much higher in the entire energy region. The maximum positions of the Ps(n) formation cross sections in our present work are in good agreement with the wave vector matching model of (Charlton 2014 J. Phys. B: At. Mol. Opt. Phys. 39, 4575). Finally, we discuss the scaling law of the Ps(n) formation cross sections with respect to the principal quantum number n of the Ps atom.