Mobilities of Mass-Identified Atomic Ions in the Noble Gases

A drift-tube—mass-spectrometer apparatus has been used to determine the mobilities of mass-identified atomic ions in the noble gases as a function of $\frac{E}{p}$ (drift field/gas pressure) at $T=295\mathrm{}$ K. The measured values of the reduced mobilities ${\mu }_0$ of ${\mathrm{He}}^{+}$ in He, ${\mathrm{Ne}}^{+}$ in Ne, and ${\mathrm{Ar}}^{+}$ in Ar are in agreement with earlier investigations that did not employ mass identification. The measured value at $\frac{E}{p}=O$, ${\mu }_0\left(H^{+} \mathrm{in}\mathrm{He}\right)=\left({31.0}_{-1.0\mathrm{}}^{+0.5\mathrm{}}\right)$ ${\mathrm{cm}}^2$ ${\mathrm{V}}^{-1\mathrm{}}$ ${\sec }^{-1\mathrm{}}$, is in good agreement with quantum-mechanical calculations, but the observed decrease of ${\mu }_0$ with ion energy is somewhat slower than that predicted by theory. The measured mobility of each of the noble-gas ions ${\mathrm{Ne}}^{+}$, ${\mathrm{Ar}}^{+}$, ${\mathrm{Kr}}^{+}$, and ${\mathrm{Xe}}^{+}$ in He is found to be $\sim \mathrm{}(6-12)\%$ lower than that of the corresponding alkali-metal ion (as determined by Tyndall's group).