The Absolute Values of the Mobility of Gaseous Ions in Pure Gases

Abstract

The absolute method of measuring the mobilities of gaseous ions developed by Tyndall and Grindley has been employed to study the ionic mobility in gases of high purity. The method was slightly altered to improve the resolving power. An intense source of high voltage x-rays previously used in recombination measurements provided an external source of ionization for the Pyrex glass mobility chamber. Under these conditions a high degree of gas purity could be maintained in the baked out chamber, and definite knowledge concerning the existence of a velocity spectrum could be obtained from the shape of experimental curves. Careful purification and drying by liquid air was employed for all gases. At time intervals of the order of 4×${10}^{-2\mathrm{}}$ seconds only a single class of each ion was found for the positive and negative ion in air. The mobility, 1.60 cm/sec. per volt/cm for the positive ion and 2.21 cm/sec. per volt/cm for the negative ion is in agreement with other absolute values. Oxygen prepared from KCl${\mathrm{O}}_3$ gave an anomalous high mobility of 2.65 for the negative ion, due probably to the presence of chlorine oxides. Oxygen from KMn${\mathrm{O}}_4$ and from a commercial tank source carefully purified gave the values 1.58 for the positive ion and 2.18 for the negative ion. Nitrogen, as finally prepared by extreme purification of the commercial tank gas gave no negative ions and a positive ion of mobility 2.09. Hydrogen was found to give no negative ions and a predominating positive ion of mobility 8.2. Indications of a higher mobility ion at 13.1 were also found. This is in agreement with the results of Loeb on ${\mathrm{Na}}^{+}$ ions in ${\mathrm{H}}_2$. Helium gave no negative ions and a positive ion of mobility 17.0. This agrees with an approximate value observed by Tyndall and Powell for lower pressures and shorter ion ages. For pure gases and ion ages of the order of magnitude of those employed in these experiments (0.04″ to 0.07″) sharp peaks, indicative of a single class of ion, were always observed.