Collision Processes Occurring in Decaying Plasmas Produced in Helium-Hydrogen Mixtures

The time dependence of the densities of ${\mathrm{He}}^{+}$, $\mathrm{He}_2^{}{}_{}{}^{+}$, ${\mathrm{H}}^{+}$,$\mathrm{H}_2^{}{}_{}{}^{+}$,$\mathrm{H}_3^{}{}_{}{}^{+}$, ${\mathrm{HeH}}^{+}$, and ${\mathrm{He}}_2$ ${\mathrm{H}}^{+}$ ions was measured in the afterglow period of plasmas produced in helium containing 0.01, 0.02, and 0.1% hydrogen for total gas pressures varying from 1 to 10 Torr. The rate constant for the ionization of ${\mathrm{H}}_2$ by $\mathrm{He}\left(2\mathrm{} {}_{}{}^3{}_{}{}^{}S\right)$ was found to be 5.2×${10}^{-11\mathrm{}}$ cm ${\sec }^{-1\mathrm{}}$. The studies resulted in the observation, for the first time, of the production of $\mathrm{H}_2^{}{}_{}{}^{+}$ by mutual collisions between metastable hydrogen molecules. The radiative lifetime of these molecules was measured to be 2.7 ± 0.2 msec. The occurence of several other collision processes was also established. The mobility of $\mathrm{H}_3^{}{}_{}{}^{+}$ in helium was determined to be ${\mu }_0=40\mathrm{}\pm 0.5$ ${\mathrm{cm}}^2$ ${\mathrm{}\left(\mathrm{V}\sec \right)\mathrm{}}^{-1\mathrm{}}$.