Energy-spectroscopic studies of electron-capture processes by low-energy, highly stripped C, N, and O ions from He

Abstract

Translation-energy spectra of charge-state-changed projectile ions scattered in the forward direction in collisions of ${\mathrm{C}}^{q+} (q=5,4)$, ${\mathrm{N}}^{q+} (q=6,5)$, and ${\mathrm{O}}^{q+} (q=6)$ ions with He atoms have been measured at collision energies of $q$ and $2q$ keV. All the product peaks observed in the spectra come from exothermic electron-capture processes. From the measured energy gains of the product ($q\ensuremath{-}1$)---charge-state ions, it has been found that an electron is captured selectively into a single shell with a particular principal quantum number $n=2$ for the incident ${\mathrm{C}}^{4+}$ ion and $n=3$ for the incident ${\mathrm{C}}^{5+}$, ${\mathrm{N}}^{5+}$, ${\mathrm{N}}^{6+}$, and ${\mathrm{O}}^{6+}$ ions. This fact is in accord with the prediction of the one-electron classical theory. It has also been revealed that there is good similarity among the energy-spectral patterns obtained for the ions having the same charge $+q$, irrespective of ionic species; such a similarity results from the similarity among diabatic potential curves for the collision systems of the $q$---charge-state ions and He. In the case of ${\mathrm{C}}^{4+}$+He collision, the two-electron---capture process into the ground state of ${\mathrm{C}}^{2+}$ occurs more efficiently than the one-electron---capture process at the low energies studied.