Dynamics of Xe44+ (6.7 MeV/A)+Ar and He collisions

The momentum vector of recoiling Ar and He target atoms ionized by Xe44+ (6.7 MeV/A) impact has been determined using high resolution recoil ion momentum spectroscopy. From the angle of emission and recoil velocity distributions of each recoil ion charge state q (q = 1 to 7 for argon ions, q = 1 and 2 for helium ions), one deduces that the recoil ions are mostly emitted backward with respect to the projectile beam direction. We show that this behavior is due to the electrons which are mainly emitted in the forward direction and thus prove, in the case of single and multiple ionization, the importance of the role played by the electrons in the momentum balance of such a collision.