Double excitation of He by fast ions

Abstract

Autoionization of He atoms following double excitation by electrons, protons, C~+ (Q =4-6), and Fo+ (Q =7-9) ions has been studied. The electron-emission yields from the doubly excited 2s ('S), 2s2p('P), and 2p ('P) states were measured at the reduced projectile energy of 1.5MeV/nucleon for observation angles between 10' and 60'. The results indicate excitation to the 2s'('S) and 2p~('D) states increases as approximately Q', while excitation to the 2s2P('P) state varies as approximately Q', where Q is the charge of the projectile. These charge dependences are significantly less than the Q dependence expected in the independent-electron model, suggesting the interaction between the two target electrons is important in creating the doubly excited states.

Multi-electron processes in atomic collisions – theory

“…The latter gives with the ®rst-order amplitude a large interference term in the transition probability proportional to 3 (Z standing for the charge of the projectile), leading to a large dierence in cross sections for protons and antiprotons. This conclusion disagree with the theoretical data of Fritsch and Lin [30] and Straton et al [33], but is in accordance with the theoretical description of the double excitation by Godunov et al including the [36] (squares). Experimental data of Moretto-Capelle et al [37] are represented by a circle and their theoretical result by a star.…”

“…These cross sections not only complete the experimental data of Giese et al [36] to lower energies, but are stated to be more exact, making sense for the comparison of dierent theoretical results with the experiment.…”

“…But the extraction of the cross sections from the experimental spectra is dicult, and needs not only a careful analysis of the involved phenomena, but a good energy resolution of the spectrometer in order to separate the peaks associated with dierent doubly excited states and to obtain information about the structure of these peaks. First Pedersen and Hvelplund [35], then Giese et al [36] have reported experimental double excitation cross sections for high velocity projectiles. But because of the insucient energy resolution of their spectrometer and the lack of measurements for backward ejection angles, the results, as stated by the authors, are not accurate enough.…”

Electron correlation in the continuum

“…Bound state solutions are calculated by damped relaxation methods. The solution of (H -E n )$ n = 0 is calculated by iterating (12) where E =< H > and V = X(l + T/fx)' 1 The filter considered here is a functional of the full Hamiltonian: any other operator could replace H, leading to projections on a different spectrum. If the individual A terms could not be disentangled, this would not be a very interesting result: the sum is usually dominated by single ionization leaving the ion in its ground state.…”

“…The quantum numbers of the final state in (24) including its allignment can be determined experimentally. Theoretical interest focusses on the competition between single and multiple step mechanisms 12 .…”