Mobilities of Atomic and Molecular Ions in the Noble Gases

Abstract

A method is described for measuring the mobilities of ions of near-thermal energy. A pulse of ions is generated in a discharge region and passes through a grid into a drift region where a uniform electric field causes the ions to move to a collector electrode. The mobilities are determined from measurements of the transit time of the ions in crossing the drift space. The experimental mobility values for thermal energy ions moving in their parent gases at 300\ifmmode^\circ\else\textdegree\fi{}K and a gas density of 2.69\ifmmode\times\else\texttimes\fi{}${10}^{19}$ atoms/cc are ${\ensuremath{\mu}}_{0}=10.5$ ${\mathrm{cm}}^{2}$/volt-sec (${\mathrm{He}}^{+}$), 20.3 (${\mathrm{He}}_{2}^{+}$), 4.0 (${\mathrm{Ne}}^{+}$), 6.5 (${\mathrm{Ne}}_{2}^{+}$), 1.60 (${\mathrm{A}}^{+}$), 2.65 (${\mathrm{A}}_{2}^{+}$), 0.90 (${\mathrm{Kr}}^{+}$), 1.21 (${\mathrm{Kr}}_{2}^{+}$), 0.58 (${\mathrm{Xe}}^{+}$), and 0.79 (${\mathrm{Xe}}_{2}^{+}$). These values are in good agreement with available theoretical results. Our measurements join smoothly at higher ion energies with the measurements made by Hornbeck and by Varney except in the case of ${\mathrm{A}}_{2}^{+}$. In addition, our results indicate that earlier measurements at near-thermal energy by Tyndall and collaborators refer to the molecular ions in helium and neon, and to the atomic ions in krypton and xenon.