STRONG ONSET OF IONIZATION IN SLOW XE-Q-XE COLLISIONS AT VERY HIGH Q()

We have discovered that ionization without accompanying electron captu re is an important process in slow (v is similar to 0.1-0.2 a.u.) Xe(q +)-Xe collisions at very high projectile charge (q >25). The measured absolute cross sections, although between one and two orders of magnit ude lower than the ones for single-electron capture, increase rapidly with q when q >25 and reach a level of approximately 1 x 10(-15) cm2 f or q >30. We argue that the reaction mechanism for ionization of the h eavier rare gases involves the formation of core-excited, autoionizing , neutral target states.