On the Nature of the Negative and Positive Ions in Air, Oxygen and Nitrogen

Abstract

Positive and Negative Ions in Air, Oxygen and Nitrogen.---(1) Mobilities just after formation were measured by using a modified form of Zeleny's blast method. Ions produced in air by polonium rays were drawn immediately by a current of 470 cm./ sec. into one side of a cross field of 130 volts/cm. and the distance they were carried along before they were dragged to the other side by the field was determined. When the average age of the ions was about 0.03 sec. the mobility was found to be the same for both positive and negative ions and equal to that for normal negative ions, about 1.89 cm./sec./volt/cm. As the age was increased to 0.5 sec., however, the positive mobility decreased to its normal value, about 1/1.40 times the negative mobility. The same results were obtained with dry commercial oxygen and nitrogen, except that the aging of the positive ion was more rapid in oxygen. (2) Nature of the ions. In explanation of the above results it is suggested that the negative ion and the initial positive ion are each one molecule in size and that the permanent positive ion is two molecules in size. This suggestion agrees with the view that when ionization occurs an electron is ejected from a molecule, leaving a positively charged molecule, an initial positive ion, which does not immediately acquire the second molecule needed to form a permanent positive ion. The electron attaches itself to a molecule and forms a permanent negative ion. It is also shown that the observed ratio of the mobilities for ions with one and two molecules respectively agrees with that computed according to the small ion theory of Wellisch.