Investigation of saddle point electrons in positron-atom ionization collisions

We investigate the appearance of fingerprints of saddle-point electrons in the ionization of atoms and molecules by positron impact. We calculate the quintuple differential cross section by means of a continuum distorted wave approximation that employs the correct kinematics. We find a clear structure located at precisely the energy and emission angle where a saddle-point electron is supposed to appear. Unmistakable signatures of this structure can also been pinpointed in the projectile dispersion and the recoiling of the target ion.