Comparison of eikonal and multiple-scattering representations of internuclear scattering in charge transfer at forward angles

In near-symmetric charge transfer at high-impact velocities and forward-scattering angles, the internuclear-scattering component of the second-order Faddeev representation of the generalized Thomas mechanisms, which, though generally associated with large-angle scattering, is valid at forward angles also, has been shown previously to agree with both the eikonal treatment in a continuum distorted-wave theory and the experimental data. A comparison of the multiple-scattering and eikonal methods using the same electronic amplitude is made in this paper. Significant differences are found between the results of the two methods, especially in the region where there is substantial cancellation among the partial amplitudes. At high velocities the Faddeev amplitude is a factor of 2 larger than the eikonal amplitude, a result attributable to the inclusion of two generalized Thomas channels in the former. The leading asymptotic form of the amplitude is also given.