Coherent treatment of transfer-excitation processes in swift ion-atom collisions

Abstract

For more than 40 years since the first ion-atom collision investigations of the two-electron process of electron transfer with excitation and its resonant and nonresonant features, a satisfactory quantum mechanical treatment has been lacking. We present now such a comprehensive transfer excitation treatment using a three-electron atomic orbital close-coupling approach within a full configuration interaction formalism, exemplified by ${\mathrm{C}}^{4+}(1{s}^{2})+\mathrm{He}$ collisions at 0.5--18 MeV impact energies. The calculated cross sections for the production of ${\mathrm{C}}^{3+}(1s2{p}^{2}\phantom{\rule{0.16em}{0ex}}^{2}D)$, which shows the strongest resonance signature among the KLL Auger transitions, are found to be in excellent agreement with zero-degree Auger projectile spectroscopy measurements covering the maximum of the resonance peak and its high energy wing. At the lower energies, the theoretical results show a second maximum which is interpreted through a nonresonant one-step transfer excitation mechanism, never considered to date. The present, fully coherent, many-body treatment provides an important advance in the modeling and understanding of multielectronic processes in quantum systems under strong and ultrafast perturbations.