The origin of the “cyanogen” bands

Abstract

There are, in addition to the line and the positive and negative band spectra of nitrogen, several other series of bands, in the production of which this element plays some part. The emission centres responsible for these bands have generally been identified with the molecules of compounds of nitrogen with other elements, though these molecules are not necessarily those of compounds which can be isolated under normal circumstances, and possibly may prove to be more of the nature of temporary associations. Such spectra include the so-called third positive band spectrum of nitrogen, the various spectra attributed to ammonia or other nitrogen-oxygen complexes, and also the cyanogen bands. The NO bands, Deslandres’ third positive group of nitrogen bands, are found in vacuum tubes filled with nitrogen, when they contain a trace of oxygen as impurity. They have also been observed in the carbon arc surrounded by a magnesia block, in uncondensed spark discharges in air and nitrogen, and in the flames of cyanogen and ammonia. They were formerly believed to be due to nitrogen alone, but Deslandres, Schniederjost, Lewis and others have proved that their production is dependent upon the presence of oxygen.