We present a theoretical study of single- and double-electron-capture (SEC and DEC) processes in ${\mathrm{O}}^{8+}+\mathrm{He}\left(1s^2\right)$ collisions over the impact-energy range of 0.1–625 keV/u using a large-scale two-active-electron semiclassical asymptotic-state close-coupling approach. Total and state-resolved cross sections for SEC and DEC into autoionization states (ADC) are obtained and benchmarked against available experimental and theoretical data. Good agreement is achieved for total SEC cross sections over the entire energy range, while the role of ADC contributions to experimentally measured single-charge-changing signals is found to be significant. True DEC cross sections are evaluated by combining state-resolved ADC cross sections with radiative stabilization branching ratios obtained from relativistic configuration-interaction calculations using the flexible atomic code. The results show that true DEC is dominated by radiative decay of asymmetric doubly excited states. The present work provides a unified description of SEC, ADC, and DEC processes and highlights the role of electron correlation and multichannel coupling in ion-atom collisions.

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• Atomic & molecular collisions
• Charge-transfer collisions