Ultra-low energy electrons from fast heavy-ion helium collisions: The target-cusp?

In collisions of fast and highly charged ions with neutral atoms the ioniza tion of the target atom is one of the most probable reactions. Therefore th e energy and angular distributions of the emitted electrons have been inves tigated for more than three decades. But up to now there are no reliable ex perimental techniques for measuring electrons with energies below E-e less than or equal to 100 meV. Over the last years we have developed a new kind of electron momentum analyser which overcomes the restrictions of the conve ntional electron spectrometers in the low energy regime. In combination of this novel electron spectrometer with a high resolution recoil ion momentum spectrometer we have performed a kinematically complete experiment investi gating the single ionization of Helium by 3.6 MeV/u Au53+ ions. The longitu dinal momentum distribution of the low energy electrons is strongly asymmet ric in the forward-backward direction due to the interaction with the long reaching coulomb potential of the outgoing highly charged projectile ion. F or the ultra-low energy electrons the momentum distribution shows a sharp m aximum at p(e) = 0.