Positronium formation in then=2 level in positron scattering from hydrogen and helium atoms

A distorted-wave model [Phys. Rev. A 27, 1904 (1983); 28, 2180 (1983)] is applied to calculate the formation of positronium in the n=2 states in $e^{+}$ scattering from hydrogen and helium atoms. The incident wave is represented by a polarized-orbital method. The first-Born-approximation results of the 2p-excited-state capture cross section in the case of helium is reported for the first time. The first Born approximation is found to be unsuitable for prediction of the rearrangement processes. The present total (ground- and excited-state) positronium-formation cross sections have been compared with the corresponding observed values of Fornari et al. [Phys. Rev. Lett. 51, 2276 (1983)] and of Charlton et al. [J. Phys. B 16, L465 (1983)].