The antiproton is a unique probe for atomic physics research. It behaves as a heavy electron or as a negative nucleus and gives a new test ground for studies of atomic collision dynamics. It is a “theoreticians’ ideal projectile” because lack of electron capture processes avoids complication in theoretical treatments, and some theoretical work is going on. Yet so far no experiment was possible at energies less than around 20 keV. With the advent of our ultra-slow antiproton beams at 10–250 eV, ionization and atomic capture processes of an antiproton projectile against various atoms “A”,
p + A -> pA+ ; A+ + e−
p + A -> (pA+)0 + e−
can be studied for the first time under the single-collision condition. This study also reveals the properties of exotic antiprotonic atoms formed in vacuo.