DOUBLE-IONIZATION OF HELIUM BY SLOW ANTIPROTONS

Coupled-states calculations with large target-centred basis sets have been used to compute ionization probabilities and cross sections for p (-) + He+ at collision energies down to 10 keV. The results are in goo d agreement with recent theoretical calculations based on numerical so lution of the time-dependent Schrodinger equation but there are no exp erimental data. Both an independent particle model and an independent event model were used to carry out calculations for p(-) + He. These r esults are in good agreement with experiment at 40 keV and above but d iffer at lower energies. The impact-parameter-dependent probabilities for these collisions were used in the independent event model to calcu late helium double-ionization cross sections and excellent agreement w as found with experimental measurements between 13 and 200 keV, but th is simple way of treating correlation fails at higher collision energi es.