Observation of interference in charge exchange scattering in He2++He+ collisions

We report the first observation of interference in charge exchange collisions between two ions. Employing the crossed-beams technique in conjunction with signal recovery methods, angular differential cross sections have been measured for charge transfer in He2+ + He+ collisions at barycentric energies between 0.5 and 10.2 keV. The oscillatory structure observed is in agreement with quantum calculations and can be interpreted in terms of interference between scattering into gerade and ungerade molecular states, which arise due to the identity of the nuclear charges.