Autoionization of He atoms following double excitation by electrons, protons, CQ+ (Q=4-6), and FQ+ (Q=7-9) ions has been studied. The electron-emission yields from the doubly excited 2s2(1S), 2s2p(1P), and 2p2(1P) states were measured at the reduced projectile energy of 1.5 MeV/nucleon for observation angles between 10°and 60°. The results indicate excitation to the 2s2(1S) and 2p2(1D) states increases as approximately Q3, while excitation to the 2s2p(1P) state varies as approximately Q2, where Q is the charge of the projectile. These charge dependences are significantly less than the Q4 dependence expected in the independent-electron model, suggesting the interaction between the two target electrons is important in creating the doubly excited states.
J. P. Giese and M. Schulz and J. K. Swenson and H. Schone and M. Benhenni and S. L. Varghese and C. R. Vane and P. F. Dittner and S. M. Shafroth and S. Datz, "Double Excitation of He by Fast Ions," Physical Review A, vol. 42, no. 3, pp. 1231-1244, American Physical Society (APS), Aug 1990.
The definitive version is available at https://doi.org/10.1103/PhysRevA.42.1231
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