State-selective double capture in collisions of bare ions with helium atoms at low energies. I. 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.