Active Nitrogen

Abstract

Criticisms have been made of the ionic theory of active nitrogen, proposed by the author some years ago, on the ground that experiments carried out since then with the specific purpose of detecting ${\mathrm{N}}_2^{+}$ ions in the glowing gas have yielded negative results. Need is felt therefore for re-examining the older theories in particular the atomic theory and its variations. It is shown in the paper that by collating the suggestions made in respect of this theory in recent years one may make the following hypothesis: Active nitrogen is a mixture of nitrogen atoms in the ground state ${}_{}{}^4{}_{}{}^{}S$ and the metastable states ${}_{}{}^2{}_{}{}^{}D$ and ${}_{}{}^2{}_{}{}^{}P$ (the last named in small proportion) produced by dissociative recombination of ${\mathrm{N}}_2^{+}$ ions and electrons always present in a strong electric discharge in nitrogen. The ${\mathrm{N}}_2^{+}$ ions and electrons are thus the parent bodies of the active substance instead of being themselves the active substance, as had been proposed in the ionic theory. The reason the production of the atoms is supposed to be due to dissociative recombination and not to electronic bombardment of ${\mathrm{N}}_2$ molecules, is that it has been known for a long time that the production of active nitrogen is closely associated with the presence and production of ${\mathrm{N}}_2^{+}$ ions. The two outstanding properties of active nitrogen (besides its chemical activity) e.g., long-duration afterglow emitting its characteristic band spectrum, and the invariable presence of ionization in the glowing gas, are thus explained as follows: The nitrogen atoms recombine by a preassociation process (as first suggested by Gaydon) to produce ${\mathrm{N}}_2$ molecules in the high vibrational levels of the $B$ state from which the first positive bands, with the characteristic intensity distribution, are emitted. The long life of the afterglow is explained as resulting from the fact that the wall recombination of the N atoms is prevented by the formation of an adsorbed layer of ${\mathrm{N}}_2$ molecules on the wall surface. (Formation of such an adsorbed layer was also assumed in the ionic theory.) The invariable presence of ionization in the glowing gas is explained as resulting from ionizing recombination of metastable atoms, $\mathrm{N}\left({}_{}{}^2{}_{}{}^{}D\right)+\mathrm{N}\left({}_{}{}^2{}_{}{}^{}P\right)\to {{\mathrm{N}}_2}^{+}+e$. Possible explanations of the negative temperature coefficient of the glow intensity, of the so-called dark modification, and also of some of the other properties of active nitrogen, are suggested.