The speed of positive ions in nitrogen

In a previous paper from this laboratory it was suggested that when helium ions move under the influence of an electric field through helium gas, the positive charge carried by an ion does not remain long associated with a single atom, but is repeatedly passed on from ion to atom at collision by the process of electron capture. This process may be regarded as equivalent to an increase in the target area presented by the atoms to the positive helium ions and must therefore lead to a reduction in their mobility. When foreign ions move in a given gas the conditions of resonance necessary for electron capture would not normally occur. If therefore in the absence of electron capture the mobility of a foreign ion in a given gas is found to afford an unambiguous measure of its mass, we may expect the value of the mobility of the ions of the gas itself to be less than that predicted from their mass, owing to the operation of this process. From the study of a number of ions in various gases we now know that helium is not a satisfactory gas in which to demonstrate the effect. Even with simple ions like Rb+, Cs+, In+, Tl+ the size of the ion has a profound effect on its mobility, so that the fact the He+ ions in helium move more slowly than the much heavier sodium ions cannot be definitely attributed to an exchange process. The exchange hypothesis offers a very probable, but not a certain, explanation of the relatively low mobility of the helium ions.