Drift Velocities of Ions in Krypton and Xenon

Abstract

Drift velocities and mobilities of ions of Kr and Xe in their respective parent gases have been measured over a wide range of values of $\frac{E}{p_0}$, the ratio of electric field strength to normalized gas pressure. Two ions appear in each gas identified as ${\mathrm{Kr}}^{+}$ and $\mathrm{Kr}_2^{}{}_{}{}^{+}$ in Kr and ${\mathrm{Xe}}^{+}$ and $\mathrm{Xe}_2^{}{}_{}{}^{+}$ in Xe. The relation that drift velocity varies as ${\left(\frac{E}{p_0}\right)}^{\frac{1}{2}}$ at high $\frac{E}{p_0}$ has been found to hold for the atomic ions and has been used to determine the equivalent hard sphere cross sections at high fields. The cross sections are 157 × ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ for Kr and 192 × ${10}^{-16\mathrm{}}$ ${\mathrm{cm}}^2$ for Xe. The Langevin theory of mobilities gives excellent agreement with experimental results extrapolated to zero field strength provided that, in the theory, the hard sphere cross section is taken as large for the atomic ions and very small for the molecular ions. The range of the polarization forces is such as to render them insignificant in atomic ion collisions and of primary importance in molecular ion collisions.