A second-order symmetric eikonal approximation for electron capture at high energies

A symmetric eikonal approximation for electron capture in ion-atom collisions at high energies has been developed within the Dodd and Greider (1966) formalism. Implicit intermediate states are included through the choice of distorted initial and final wavefunctions as in previous work by Maidagan and Rivarola (1984). Explicit intermediate states are considered by the introduction of a free-particle Green's function G 0 + . Thus, when K-K shell processes are studied, the Thomas peak is described by differential cross sections at high energies and the correct asymptotic high-velocity limit is obtained for total cross sections. The model is applied for the resonant charge in H + +H(ls) collisions. Also, the characteristic dip of the continuum distorted-wave model of Cheshire (1964) is analysed when higher orders are included at 'realistic' high energies.