Associative Detachment of ${\mathrm{O}}^{-}$ with CO, ${\mathrm{H}}_2$, and ${\mathrm{O}}_2$

The associative detachment reactions of ${\mathrm{O}}^{-}$ with CO, ${\mathrm{H}}_2$, and ${\mathrm{O}}_2$ are studied experimentally using an ion beam (0-10 eV) impinging on a gas-filled chamber. The resultant electrons are energy analyzed using retarding potentials. At low ion energy, cross sections for total electron detachment for the reactions of ${\mathrm{O}}^{-}$ with CO and ${\mathrm{H}}_2$ vary as the inverse of the relative velocity. At higher energies, the cross sections show a broad peak. We interpret this shape in terms of the potential-energy curves of the compound states. The energy distributions for the electrons resulting from the reactions of ${\mathrm{O}}^{-}$ with CO and ${\mathrm{H}}_2$ exhibit peaks at low energy corresponding to the excitation of high vibrational and rotational states of the resultant triatomic molecules (C${\mathrm{O}}_2$, ${\mathrm{H}}_2$O). Progressions observed in these distributions have spacings corresponding to the preferential excitation of the bending modes of the triatomic molecules. The cross section for total electron detachment for the reaction of ${\mathrm{O}}^{-}$ with ${\mathrm{O}}_2$ exhibits a threshold near 0.7 eV and rises linearly at higher energy.