Associative ionization in hydrogen atom-rare gas collisions between 10 and 100 eV

We have observed the process of associative ionization (AI) in collisions between hydrogen and rare gas atoms both prepared in their ground states (H + XXH+ + e- with X = Ar,Kr,Xe). This is the first experimental observation of this process, which we compare to the other charge-producing cross sections reported previously. AI takes place only in a small region of collision energies close to threshold. The cross sections show a distinct maximum, with a typical value of about 2×10-19 cm2. In contrast to the heavier rare gases AI is not observed in collisions of atomic hydrogen with He and Ne.