Double electron capture and the angular distribution of ejected electrons inNe8+-He collisions

Double-electron-capture cross sections to individual doubly excited states and autoionizing electron spectra at fixed angles for ${\mathrm{Ne}}^{8+}$-He collisions are calculated and analyzed for collision energies from 20 to 80 keV/amu. An independent-electron approximation is adopted where the amplitudes for double capture are derived from the antisymmetrized product of single-electron-capture amplitudes properly weighted with configuration-interaction coefficients. By choosing the quantization axis to be perpendicular to the collision plane, we also study the propensity rule for the M distribution of the cross section for each doubly excited state. The electron spectra at 0° are compared with experiments. At 80 keV/amu collision energy, our theoretical spectrum agrees with experiment very well. At lower energies, the agreements are not as good, but the dominant features are well predicted.