Approximate triangle amplitude for three-body charge exchange processes

The single-rescattering contribution to the amplitude pertaining to three-body charge exchange reactions (triangle amplitude) contains the off-shell Coulomb T-matrix T^C describing the intermediate-state Coulomb scattering of charged subsystems. For ease of computation, the latter is usually replaced by the potential V^C which, however, is unsatisfactory in many cases. An alternative approximation, obtained by ‘‘renormalizing’’ the ‘‘triangle’’ contribution with V^C instead of T^C by a simple analytic expression, is shown to yield results in excellent agreement with the numerically calculated exact amplitude, for atomic elastic exchange reactions, over a wide range of (medium to high) projectile energies and scattering angles (including the forward direction). © 1996 The American Physical Society.