DOUBLE-EXCITATION OF HE BY MULTIPLY-CHARGED IONS

We have studied double excitation of He by 1.5 MeV/amu protons, antiprotons, He2+, Li3+, C6+ and F9+, and 500 keV/amu He2+ and Li3+. For this purpose we have performed single-centre close-coupling calculations which allow for a simultaneous description of double excitation, ionization and, therefore, coherence between these processes. We have analysed the validity of the Born series to provide the cross section dependence on the projectile charge Z(P). In particular, we show that, at 1.5 MeV/amu, the Born II approximation describes reasonably well excitation to the S-1(e)(2s(2)), (1)p(o)(2s2p) and D-1(e)(2p(2)) resonances for Z(P) = -1 and Z(P) = 1. On the other hand, the Born II approximation fails in describing excitation to the S-1(e) and P-1(o) resonances for Z greater than or equal to 2.