Abstract
This study focuses on the details of cascade repopulation of doubly excited triply open-shell C3+(1s2s2p)4P and 2P± states produced in 2–18 MeV collisions of C4+(1s2s3S) with He. Such cascade calculations are necessary for the correct determination of the ratio R of their cross sections, used as a measure of spin statistics [Madesis et al. PRL 124 (2020) 113401]. Here, we present the details of our cascade calculations within a new matrix formulation based on the well-known diagrammatic cascade approach [Curtis, Am. J. Phys. 36 (1968) 1123], extended to also include Auger depopulation. The initial populations of the 1s2snℓ4L and 1s2snℓ2L levels included in our analysis are obtained from the direct nℓ single electron capture (SEC) cross sections, calculated using the novel three-electron close-coupling (3eAOCC) approach. All relevant radiative branching ratios (RBR) for n≤4 were computed using the COWAN code. While doublet RBRs are found to be very small, quartet RBRs are found to be large, indicating cascade feeding to be important only for quartets, consistent with previous findings. Calculations including up to third order cascades, extended to n→∞ using an n−3 SEC model, showed a ∼60% increase of the 1s2s2p4P populations due to cascades, resulting, for the first time, in R values in good overall agreement with experiment.
Highlights
Excited atomic and ionic states can be produced in ion-atom and ion-electron collisions by various processes such as inner-shell excitation, ionization, electron capture, and/or their combinations
We showed that only a new dynamical calculation involving three active electrons is found to give results consistent with experiment, with radiative cascade repopulation playing an important role
We present our radiative branching ratios (RBR) results based on the COWAN code calculations, as well as the initial production cross sections based on our 3eAOCC approach
Summary
Excited (autoionizing) atomic and ionic states can be produced in ion-atom and ion-electron collisions by various processes such as inner-shell excitation, ionization, electron capture (to excited states), and/or their combinations These states relax to lower energy states and the ground state via radiative and/or Auger decays in a stepwise manner, known as cascades, resulting in the repopulation of the intermediate levels. In the case of 2p single electron capture (SEC) in collisions of 1s2s 3S ions with He and H2 , R has been considered to be an indicator of spin statistics [31,32,33,34,35] This ratio results in R = 1, when considering only spin multiplicity, while R = 2 in the frozen core approximation, where only the 4P and a single 2P state can be produced from the 1s2s 3S initial state [34,36,37]. The necessary radiative and Auger transition rates were computed using the COWAN [39] atomic structure code, while the initial state populations were taken from our recent publication [30], where they were computed using the new three-electron atomic orbital close-coupling (3eAOCC) approach
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