Low-Field Drift Velocities and Reactions of Nitrogen Ions in Nitrogen

Abstract

Drift velocities and reactions of nitrogen ions have been investigated at 300°K at values of $\frac{E}{N}$ (the ratios of electric field to number density) between 1.5 and 20×${10}^{-16\mathrm{}}$ V ${\mathrm{cm}}^2$, and at pressures between 0.5 and 1 Torr. Ions were produced in a glow discharge and were gated into a drift cell, withdrawn through a slit, and their mass and intensity were determined as a function of the drift time by a mass analyzer. Comparison of experimental results with theoretical calculations allowed the determination of true drift velocities and reaction rates for ions undergoing reaction during the drift time. The ions in nitrogen were found to occur in two groups, $\mathrm{N}_2^{}{}_{}{}^{+}$-$\mathrm{N}_4^{}{}_{}{}^{+}$ and ${\mathrm{N}}^{+}$-$\mathrm{N}_3^{}{}_{}{}^{+}$, such that interactions within the groups are much faster than any interactions between the groups. Rate constants for the reaction $\mathrm{N}_2^{}{}_{}{}^{+}$+${\mathrm{N}}_2$+${\mathrm{N}}_2$→$\mathrm{N}_4^{}{}_{}{}^{+}$+${\mathrm{N}}_2$ were found to vary from 7×${10}^{-29\mathrm{}}$ to 2×${10}^{-29\mathrm{}}$ ${\mathrm{cm}}^6$/sec between $\frac{E}{N}$ of 5×${10}^{-16\mathrm{}}$ and 18×${10}^{-16\mathrm{}}$ V ${\mathrm{cm}}^2$, while for the reverse reaction the rates varied from 0.3×${10}^{-13\mathrm{}}$ to 110×${10}^{-13\mathrm{}}$ ${\mathrm{cm}}^3$/sec. The pressure dependences of the reaction rates were consistent with a three-body forward reaction and a two-body reverse reaction over our limited pressure range. For the ${\mathrm{N}}^{+}$-$\mathrm{N}_3^{}{}_{}{}^{+}$ system, the interaction of ${\mathrm{N}}^{+}$ with the neutral gas to produce $\mathrm{N}_3^{}{}_{}{}^{+}$ was observed at $\frac{E}{N}=5\mathrm{}\times {10}^{-16\mathrm{}}$ V ${\mathrm{cm}}^2$ with a rate constant of 3×${10}^{-29\mathrm{}}$ ${\mathrm{cm}}^6$/sec. No reactions could be positively identified which produced ${\mathrm{N}}^{+}$ over the range of our experimental parameters.