Electron capture in low-energy collisions of Cq+ and Oq+ with H and H2

Abstract

Total electron-capture cross-section measurements are reported for ${\mathrm{C}}^{q+} \left(3\mathrm{}\le q\le 6\right)$ and ${\mathrm{O}}^{q+} \left(2\mathrm{}\le q\le 6\right)$ ions colliding with hydrogen atoms and molecules in the energy range ($0.01\le E\le 10$) keV/amu. The cross sections range from (0.5-7)×${10}^{-15\mathrm{}}$ ${\mathrm{cm}}^2$, and neither obey simple charge-scaling rules, nor exhibit uniform dependences on collision velocity in this energy range. For a given charge $q$, cross sections for the less-highly-stripped oxygen ions exceed those for carbon ions at energies below a few-hundred eV/amu. Comparison is made between these measurements and theoretical calculations which have heretofore remained untested at low collision energies. In general, the agreement is good for those systems where detailed perturbed-stationary-state theory is available, but is best with those calculations in which the collision dynamics as well as the molecular couplings are treated quantum mechanically. Generalized theories which work well for collision systems containing many bound electrons, do not give accurate representations of these few-electron systems at low energies.