Ion Production and Loss Processes in Helium-Nitrogen Mixtures

Detailed studies of the time dependence of the number density of ions have been made during the decay period of plasmas produced in He containing various concentrations of nitrogen molecules. Various reaction-rate constants were obtained: $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)+{\mathrm{N}}_2\to \mathrm{N}_2^{}{}_{}{}^{+}+\mathrm{He}+e\left[\right(6.3\mathrm{}\pm 1.0)\times {10}^{-11\mathrm{}} {\mathrm{cm}}^{3}invsec]$; ${\mathrm{N}}_2^{+}$ + ${\mathrm{N}}_2$ + He → ${\mathrm{N}}_4^{+}$ + He [(5.3 ± 0.3) × ${10}^{-30\mathrm{}}$ ${\mathrm{cm}}^6$ ${\sec }^{-1\mathrm{}}$] and ${\mathrm{N}}^{+}$ + ${\mathrm{N}}_2$ + He → ${\mathrm{N}}_3^{+}$ + He [(4.6 ± 0.4) × ${10}^{-29\mathrm{}}$ ${\mathrm{cm}}^6$ ${\sec }^{-1\mathrm{}}$]. Evidence for the charge-transfer process ${\mathrm{N}}_2^{+}$ + N → ${\mathrm{N}}^{+}$ + ${\mathrm{N}}_2$ was obtained. The values of the ambipolar-diffusion coefficients of nitrogen ions in He were found to be $D_a{p}_0\left({\mathrm{N}}^{+}\right)=970\mathrm{}\pm 50$; $D_a{p}_0\left(\mathrm{N}_2^{}{}_{}{}^{+}\right)=920\mathrm{}\pm 40$, and $D_a{p}_0\left(\mathrm{N}_3^{}{}_{}{}^{+}\right)=840\mathrm{}\pm 70$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ Torr, while the diffusion coefficient of $\mathrm{He}\left(2\mathrm{}{}_{}{}^3{}_{}{}^{}S\right)$ was $D_m{p}_0=480\mathrm{}\pm 30$ ${\mathrm{cm}}^2$ ${\sec }^{-1\mathrm{}}$ Torr.