E+-H- 4-PARTICLE THRESHOLD BREAK-UP

Wannier threshold theory is applied to the four-particle break-up of H - by positron impact. The escape of two electrons and a positron intro duces an interesting feature into the Wannier formalism: the possibili ty of multiple threshold configurations each with a characteristic ene rgy dependence for excitation. Moreover, because the centre of charge and centre of mass are displaced from one another, the system requires a distinction to be made between configurations which may have identi cal potential energies but different excitation energies, i.e. between Coulomb correlations and Coulomb dynamics. The energy dependence of t he threshold cross section is derived through the introduction of gene ralized coordinates and the determination of the system's unstable nor mal modes of oscillation.