Absolute integral cross sections have been measured for associative ionization reactions involving the ${\mathrm{C}}^{-}$ and ${\mathrm{C}}^{+}$, ${\mathrm{N}}^{+}$, and ${\mathrm{O}}^{+}$ reactants. These measurements, obtained using a merged-beam setup in the keV range, provide us with useful experimental information on the efficiency and mechanisms of molecular ion formation from ionic reactants. The relative magnitudes of the different cross sections are rationalized by considering the spin multiplicities of initial and final states, and the exothermicities of the detachment and transfer ionization channels. The very different production efficiencies of $\mathrm{C}{\mathrm{O}}^{+}$ ions via the ${\mathrm{O}}^{-}+{\mathrm{C}}^{+}$ and ${\mathrm{C}}^{-}+{\mathrm{O}}^{+}$ channels are explained by statistical and energetic considerations. The potential energy curves of CO and $\mathrm{C}{\mathrm{O}}^{+}$ have been calculated by quantum ab initio methods in order to characterize the reactive pathways leading to autoionization. Thermal rate coefficients are derived to serve the plasma physics community.

• Received 20 June 2008

DOI:https://doi.org/10.1103/PhysRevA.78.062705