Double excitation of He by fast ions

Autoionization of He atoms following double excitation by electrons, protons, C{sup {ital Q}+} ({ital Q}=4--6), and F{sup {ital Q}+} ({ital Q}=7--9) ions has been studied. The electron-emission yields from the doubly excited 2{ital s}{sup 2}({sup 1}{ital S}), 2{ital s}2{ital p}({sup 1}{ital P}), and 2{ital p}{sup 2}({sup 1}{ital P}) states were measured at the reduced projectile energy of 1.5 MeV/nucleon for observation angles between 10{degree} and 60{degree}. The results indicate excitation to the 2{ital s}{sup 2}({sup 1}{ital S}) and 2{ital p}{sup 2}({sup 1}{ital D}) states increases as approximately {ital Q}{sup 3}, while excitation to the 2{ital s}2{ital p}({sup 1}{ital P}) state varies as approximately {ital Q}{sup 2}, where {ital Q} is the charge of the projectile. These charge dependences are significantly less than the {ital Q}{sup 4} dependence expected in the independent-electron model, suggesting the interaction between the two target electrons is important in creating the doubly excited states.