Ion-Ion Mutual Neutralization Cross Sections Measured by a Superimposed Beam Technique

Ion-ion neutralization cross sections have been measured for ${\mathrm{N}}^{+}$ + ${\mathrm{O}}^{-}$, ${\mathrm{N}}_2^{+}$ + ${\mathrm{O}}_2^{-}$, and ${\mathrm{O}}_2^{+}$ + ${\mathrm{O}}_2^{-}$. The kinetic energy range, in the barycentric coordinate system covered by the experiment, is between 0.1 and 98 eV with an energy resolution of about 0.1 eV. The products of the neutralization cross section $Q$ times the relative speed $v_{\mathcal{r}}$ are nearly independent of energy, having values close to ${10}^{-7\mathrm{}}$ ${\mathrm{cm}}^3$/sec for all three systems studied, except that below 0.5 eV the ${\mathrm{N}}^{+}$ + ${\mathrm{O}}^{-}$ and ${\mathrm{N}}_2^{+}$ + ${\mathrm{O}}_2^{-}$ systems show a rapid increase of $Q{v}_{\mathcal{r}}$ with decreasing energy. The experiment employs the superposition of positive- and negative-ion beams of several keV energy over a common path length of 33 cm. The beams are subsequently separated and the neutral products of the reaction are measured.