Résumé : The treatment of overall Coulomb interactions in momentum-space calculations of inelastic atomic collisions is discussed and a generalization of the Vincent-Phatak procedure is presented. An application to the formation of Ps - in Ps collisions with H(1s) is given, based on a two-state one-electron model in the energy range 13.5 to 180 eV. © 1995 IOP Publishing Ltd.