The Recombination of Ions in Argon, Nitrogen and Hydrogen

Since free electrons are known to exist in ionized A, ${\mathrm{N}}_2$ and ${\mathrm{H}}_2$ these gases are employed in an effort to measure directly the coefficient of recombination for positive ions and electrons. At the same time the coefficient is determined for positive and negative ions in ${\mathrm{H}}_2$ which would be expected theoretically to differ from other gases. The method is one using x-rays as the ionizing agent and has already been described by L. C. Marshall and the writer. Previous indirect methods and theory indicate that $\alpha$, the coefficient of recombination for ions and electrons is of the order of ${10}^{-10\mathrm{}}$ compared to ${10}^{-6\mathrm{}}$ for positive and negative ions. In the present work results similar to those in air are obtained in the pure gases, and only a slight change in $\alpha$ is observed when sufficient ${\mathrm{O}}_2$ is added to cause immediate attachment of the free electrons. Further direct tests in pure A, ${\mathrm{N}}_2$ and ${\mathrm{H}}_2$ indicate that negative ions are present in large quantities at all times, although a constant number of free electrons is also present. Hence it is probable that recombination was taking place between positive and negative ions rather than positive ions and electrons. It is assumed that as a result of the action of the ionizing agent negative ions are formed by attachment to excited metastable molecules in the case of A and ${\mathrm{N}}_2$ and by attachment to atoms or triatomic molecules in the case of ${\mathrm{H}}_2$.