Ion-Molecule Reactions betweenO−andO2at Thermal Energies and Above

Abstract

The rate coefficients for the reactions of ${\mathrm{O}}^{-}$ ions with ${\mathrm{O}}_2$ molecules have been measured in a drift-tube mass spectrometer at 300 °K as a function of $\frac{E}{N}$, the ratio of the electric drift field to the gas number density. Two different measurement techniques were employed. One technique was based on the observation of the attenuation of the parent ${\mathrm{O}}^{-}$ ion species with increasing drift distance; the other involved examination of the shape of the product ion arrival-time spectra. The rate coefficient for the reaction ${\mathrm{O}}^{-}$ + ${2\mathrm{O}}_2$ → ${\mathrm{O}}_3^{-}$ + ${\mathrm{O}}_2$ was measured on the $\frac{E}{N}$ range 6-29 × ${10}^{-17\mathrm{}}$ V ${\mathrm{cm}}^2$. The rate coefficient was found to be (1.0 ± 0.2) × ${10}^{-30\mathrm{}}$ ${\mathrm{cm}}^6$/sec over the entire $\frac{E}{N}$ range. The reaction ${\mathrm{O}}^{-}$ + ${\mathrm{O}}_2$ → ${\mathrm{O}}_2^{-}$ + O was observed with a rate that increased sharply with $\frac{E}{N}$. The rate coefficient was found to increase from (2.5 ± 1.5) × ${10}^{-14\mathrm{}}$ ${\mathrm{cm}}^3$/sec at an $\frac{E}{N}$ of 63 × ${10}^{-17\mathrm{}}$ V ${\mathrm{cm}}^2$ to a value of (3.4 ± 1.0) × ${10}^{-12\mathrm{}}$ ${\mathrm{cm}}^3$/sec at an $\frac{E}{N}$ of 140 × ${10}^{-17\mathrm{}}$ V/${\mathrm{cm}}^2$.