The Relative Mobility of Initial Positive Ions in Gas Mixtures at Low Pressures

The relative mobilities of the initial positive ions in gas mixtures at pressures of 30 to 60 mm have been determined for mixtures of ${\mathrm{C}}_2$ ${\mathrm{H}}_5$Cl and ${\mathrm{H}}_2$, ${\mathrm{N}}_2$ and ${\mathrm{H}}_2$, and ${\mathrm{N}}_2$ and ${\mathrm{C}}_2$ ${\mathrm{H}}_5$Cl, using the Franck-Rutherford alternating potential method and ions produced by $\alpha$-rays of polonium. High frequency potential generated by a Hartley oscillator was used so as to insure that the age of the ions was only a fraction of a second. In each case two types of ions were detected, for which the ratio of the mobilities came out equal to the inverse ratio of the square root of the molecular weights. These ratios were found to be independent of the relative amounts of the gases present, although the absolute values of the mobilities changed. This would seem to indicate that the initial mobility at low pressures is determined chiefly by the mass of the ion rather than by its dimensions. The fact that aged ions have lower mobilities indicates that they are clusters.