The single- and double-electron capture processes in ${\mathrm{Ne}}^{8+}+\mathrm{He}$ collisions are investigated using a two-active-electron semiclassical atomic-orbital close-coupling method in the energy range from 0.2 to 100 keV/u. A sufficiently large basis set with 98 and 19 Gaussian-type orbitals in ${\mathrm{Ne}}^{8+}$ and He, respectively, is employed to include electron-electron correlation and the coupling of numerous autoionizing channels. Total and $nl$ state-selective single-electron-capture cross sections show excellent agreement with available experimental data. The double-electron-capture cross sections for the $3ln{l}^{\prime }(n=3-5)$ channels, which contribute 30%–40% to the total single-electron-capture cross sections through postcollision autoionization, are reported. Further analysis reveals that electron correlation and the coupling between single- and double-capture channels significantly affect the cross sections by a factor of 2–3 for subdominant single-capture channels and double-capture autoionization states. The x-ray spectra and the Auger-electron spectra from double capture to autoionizing states are simulated and successfully reproduce the fundamental features of the experimental data, which indicates that at a collision energy of 20 keV/u, previous single-active-electron theoretical calculations significantly underestimated the cross sections for weak double-electron capture channels, including the $3s3d{}^{1}D^e, 3s3p{}^{1}P^o, 3p3d{}^{1}D^o$, and $3p^2{}^{1}D^e$ states.

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• Atomic & molecular collisions