Infra-Red Bands in the Aurora

Abstract

IN his letter in these columns¹ regarding the infrared aurora spectrum observed by Vegard, Jevons failed to say anything about an intensity phenomenon in the first positive bands of nitrogen to which I first directed attention in a note in the Physical Review.² I called this phenomenon the variation of intensity within a progression, the progression in this case being a ‘v’ progression. It is strikingly demonstrated in Lord Rayleigh's³ experiments on the afterglow in mixtures of nitrogen and the rare gases. In this paper Lord Rayleigh suggested that the auroral radiation of wave-length 6323 A. was probably the first positive nitrogen band (10, 7). In directing attention to Lord Rayleigh's experiments, I pointed out that his results could be interpreted as either real or apparent violations of the Franck-Condon rule for band intensities. Recently, a similar result in iodine, namely, the observations of Ramsauer on the quenching of a fluorescence series in an iodine-oxygen mixture, was explained by Loomis and Fuller,⁴ who suggested that the effect was due to irregular reabsorption of the fluorescent light. The irregularity of the reabsorption was explained by enhanced predissociation in the upper electronic state. A similar explanation could apply just as well to nitrogen, since enhanced predissociation is produced in the upper electronic state of the first positive bands in the presence of rare gases. In both iodine and nitrogen the phenomenon of variation of intensity in a ‘v’ progression would have to be interpreted as an apparent violation of the Franck-Condon rule.