Single- and double-electron-capture processes in the collisions of C 4+ ions with He

The nonradiative single-electron-capture (SEC) and double-electron-capture (DEC) processes for C${}^{4+}$(1${s}^{2}$) colliding with He atoms are investigated by using the quantum-mechanical molecular-orbital close-coupling method. Total and state-selective electron-capture cross sections are calculated in the energy range of 10${}^{\ensuremath{-}6}$--6 keV/amu. For energies less than 2 keV/amu, the DEC dominates the electron-capture processes. As the energy increases, the SEC cross sections increase while the DEC cross sections decrease; when $E$ > 2 keV/amu, the SEC process becomes the dominant mechanism. It is found that the SEC processes mainly result from the electron capture to $n$ = 3 channels of C${}^{3+}$ ion for energy below 0.7 keV/amu and from $n$ = 2 channels for $E>0.7$ keV/amu. Compared with the available theoretical calculations, better agreement is achieved between the present results and the available measurements for total DEC and SEC cross sections. For state-resolved cross sections, excellent agreement is obtained for two-electron capture to C${}^{2+}$(2${s}^{2}$), C${}^{2+}$(2$s$2$p$), and C${}^{2+}$(2${p}^{2}$) and one-electron capture to C${}^{3+}$(2$s$) and C${}^{3+}$(2$p$) between the present calculations and the available theoretical and experimental results.