e+ + H(ns) → Ps(n's) + p for arbitrary n and n'

Positronium (Ps) formation in an arbitrary s-state from an arbitrary s-state of the hydrogen atom by positron impact has been studied within the framework of distorted-wave theory (DWT) which has recently been derived by the authors. A general formula for obtaining partial-wave distorted-wave amplitudes of positronium formation for all such reactions has been derived in closed analytic forms. This general formalism has then been used to obtain the results for differential and total cross sections in the energy range 20-300 eV. Further, in order to derive the general formula for scattering amplitudes in a closed analytic form, a simple prescription has been made to evaluate the arbitrary order derivatives of the general three- denominator Lewis integral. To the best of our knowledge, the distorted-wave results for the differential and total cross sections for such reactions are reported for the first time in the literature