TRIANGLE DIAGRAM WITH OFF-SHELL COULOMB T-MATRIX FOR (IN-)ELASTIC ATOMIC AND NUCLEAR 3-BODY PROCESSES

The driving terms in three-body theories of elastic and inelastic scat tering of a charged particle off a bound state of two other charged pa rticles contain the fully off-shell two-body Coulomb T-matrix describi ng the intermediate-state Coulomb scattering of the projectile with ea ch of the charged target particles. Up to now the latter has usually b een replaced by the Coulomb potential, either when using the multiple- scattering approach or when solving three-body integral equations. Gen eral properties of the exact and the approximate on-shell driving term s are discussed, and the accuracy of this approximation is investigate d numerically, both for atomic and nuclear processes including bound-s tate excitation, for energies below and above the corresponding three- body dissociation threshold, over the whole range of scattering angles .