New Green Band System of N₂ and Conditions of Excitation

Abstract

GAYDON¹, in a recent paper on a new Green band system of nitrogen, has made some observations concerning the effect of excitation on the intensity distribution, from which he concludes that the new bands are a consequence of ionic rather than electron-collision excitation. He bases his conclusions on the results of Smyth and Arnott² on the vibrational intensity distribution in the N₂ band systems. It appears that Gaydon had not seen a more recent investigation of Tawde³ on the intensities in the second positive system of nitrogen. The results of Smyth and Arnott are merely the visual and densito-meter estimates of photographic blackenings ; while those of Tawde are the accurate quantitative intensity values of bands derived by rigorous methods of photographic photometry expressed in terms of energy units of a calibrated standard lamp. It has been shown by the present author and his collaborators⁴ in several papers that mere visual or densitometer estimates can be wrong by several percent. Hence it is doubtful how far the view put forward by Gaydon regarding the mechanism of the excitation of the new bands can be sustained.