Signature of Single Binary Encounter in Intermediate Energy He^2+–Ar Collisions^*

We experimentally observe the signature of electron emission resulting from a single binary encounter mechanism in the intermediate collision energy regime of 30 keV/u He^2+ on argon. Electron emission spectra in the transfer ionization are obtained and compared with classical calculations from a two-step model considering the initial electron velocity and re-scattering of the binary encounter electron in the recoil potential. Although the present reaction is actually a four-body problem, the model starting from a binary encounter gives out surprisingly good agreement with the experimental data. Our studies show that orbital velocities of the electron affect the emission patterns of ionized electrons significantly.