STATE-SELECTIVE DOUBLE CAPTURE IN COLLISIONS OF BARE IONS WITH HELIUM-ATOMS AT LOW ENERGIES .1. TOTAL CROSS-SECTIONS

Double capture cross sections to individual doubly excited states for collisions between bare ions of carbon and oxygen with helium atoms in the energy range of a few keV amu-1 are calculated. By adopting an independent-electron approximation, the capture probability to each doubly excited state is calculated in terms of products of single capture amplitudes properly weighted with configuration-interaction coefficients, while the single capture amplitudes are calculated using a two-centre atomic orbital close-coupling expansion method with an extended basis set. The resulting cross sections are compared with recent results from high-resolution Auger electron measurements to assess the validity of the independent-electron approximation as well as the mechanism of double capture. It is shown that there is qualitative agreement between the present results and experiments.