Projectile excitation to autoionizing states in swift collisions of open-shell He-like ions with helium

Atomic orbital close-coupling calculations involving three active electrons within a full configuration interaction formalism are used to investigate projectile excitation. Cross sections for the production of the autoionizing (2s2p0.16em0ex³P) states in 0.5--1.5 MeV/u collisions of C⁴⁺(1s2s0.16em0ex³S) and O⁶⁺(1s2s0.16em0ex³S) ions with He are presented. Results are compared to accompanying 0^∘ Auger projectile spectroscopy measurements. While the projectile energy dependence of the theoretical results is in overall agreement with experiment, theory is found to be somewhat smaller than experiment. Critical comparisons to first-order Born and a minimal basis close-coupling calculation indicate that the use of low-order perturbative treatments and related interpretations may be questionable in this energy range. Such a nonperturbative treatment, which does not rely on any scaling parameters or renormalization, is seen to provide an important advance in the modeling of multielectron multi-open-shell quantum systems under ultrafast perturbations, whose understanding seems to still be incomplete.