Drift Velocities and Interactions of Negative Ions in Oxygen

Abstract

Drift velocities and reactions of negative ions have been investigated in oxygen at temperatures between 310 and 370 °K at values of $\frac{E}{N}$ (the ratio of electric field to neutral-gas number density) between 2 and 400 × ${10}^{-17\mathrm{}}$ V ${\mathrm{cm}}^2$, and at pressures ($P_0$) between 0.5 and 4 Torr. Electrons were produced from a hot filament and reacted with the neutral-gas molecules to produce ions. The ions were then gated into a drift cell through a double grid, withdrawn through an aperture, and their mass and intensity were determined as a function of drift time by a quadrupole mass analyzer and a gated particle multiplier. Comparison of experimental results with numerical calculations allowed the determination of ion drift times and reaction rates. The rate constant for the reaction ${\mathrm{O}}^{-}+{\mathrm{O}}_2+{\mathrm{O}}_2\to {\mathrm{O}}_3^{-}+{\mathrm{O}}_2$ was found to be 9 × ${10}^{-31\mathrm{}}$ ${\mathrm{cm}}^6$/sec at low $\frac{E}{N} (<\mathrm{}30\mathrm{}\times {10}^{-17\mathrm{}} \mathrm{V} {\mathrm{cm}}^2)$. At higher $\frac{E}{N} (>\mathrm{}70\mathrm{}\times {10}^{-17\mathrm{}} \mathrm{V} {\mathrm{cm}}^2)$ the reaction ${\mathrm{O}}^{-}+{\mathrm{O}}_2\to {\mathrm{O}}_2^{-}+\mathrm{O}$ was observed with a rate that increased sharply with $\frac{E}{N}$ to a value of 5 × ${10}^{-11\mathrm{}}$ ${\mathrm{cm}}^3$/sec at $\frac{E}{N}=300\mathrm{}\times {10}^{-17\mathrm{}}$ V ${\mathrm{cm}}^2$.