THRESHOLD IONIZATION OF HYDROGEN BY ANTIPROTON IMPACT

Antiproton impact ionization near threshold is analysed from the point of view of an unstable dynamical equilibrium in the slow three-body b reak-up configuration. The instability is shown to be displaced from t he Coulomb saddle-the centre of charge of the antiproton and the elect ron-and hence with the proton on the line between the negative pair bu t about sir times closer to the antiproton than to the electron. The W annier threshold law is derived, and possible negative-ion probes of t hese underlying Coulomb instabilities considered.