DYNAMICS OF XE44+ (6.7 MEV A)+AR AND HE COLLISIONS/

The momentum vector of recoiling Ar and He target atoms ionized by Xe4 4+ (6.7 MeV/A) impact has been determined using high resolution recoil ion momentum spectroscopy. From the angle of emission and recoil velo city distributions of each recoil ion charge state q (q = 1 to 7 for a rgon ions, q = 1 and 2 for helium ions), one deduces that the recoil i ons are mostly emitted backward with respect to the projectile beam di rection. 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.