Hyperspherical approach to double-electron excitation of He by fast-ion impact. II. Excitation to the (2l3l') and (3l3l') manifolds by proton and antiproton impact.

Abstract

Double-electron excitation process of He atoms from the ground state to the manifolds of the doubly excited 2l3l' and 3l3l' states by proton and antiproton impact have been theoretically investigated using a close-coupling method at the 1.5-MeV/u energy regime. The semiclassical impact-parameter method with a straight-line-trajectory approximation is employed to describe collision processes. Hyperspherical wave functions are adopted to take full account of strongly correlated motion of two atomic electrons in He. The difference between the cross section by proton impact and that by antiproton impact is small except for the process to the 3p3p $^{1}$${\mathit{S}}^{\mathit{e}}$ state. The reason for the small difference between \ensuremath{\sigma}(p) and \ensuremath{\sigma}(p\ifmmode\bar\else\textasciimacron\fi{}) is discussed. The $^{1}$${\mathit{P}}^{0}$ states are found to play an important role as intermediate ones. For the process to the doubly excited 2l3l' states, the (2s3p+3s2p${)}^{1}$${\mathit{P}}^{0}$ state plays a crucial role. For the excitation process to the 3l3l' states, the ratio of the second-order process to the first-order one is larger than that in the case of the process to the 2l2l' and 2l3l' states, suggesting that the difference between the mechanism of the excitation to the (2l,2l') and (2l,3l') manifolds and that to the (3l,3l') manifold arises from the smaller overlap of the (3l,3l') wave functions with that of the ground state. It is seen that the physical interpretation of the results based on the rovibrator model of the doubly excited states gives a deeper physical insight into the mechanism of the double-electron excitation.