Further spectra associated with carbon

• Published in: Proceedings of the Royal Society of London. Series A, Containing papers of a mathematical and physical character Containing papers of a mathematical and physical character, 1925-06, Vol.108 (746), p.343-355
• Main Author: Johnson, R. C.
• Format: Article
• Language: English
• Subjects: Carbon; Helium; Line spectra; Low pressure; Molecular spectra; Molecules; Nitrogen; Spectral bands
• ISSN: 0950-1207; 2053-9150
• DOI: 10.1098/rspa.1925.0080

In a recent paper by Professor Merton and myself, an investigation was made of the experimental conditions effecting the isolation of some familiar band-spectra of Carbon. In particular, we made a study of the action of Helium in isolating and modifying spectra associated with this element. It was found that under appropriate conditions some new spectra of Carbon were isolated. With a trace of an oxide of Carbon in some 20 to 30 mm. of Helium an uncondensed discharge produced a band system identical with that found by Pluvinet and Baldet in the spectrum of comet tails, and which was afterwards discovered by Fowler to be characteristic of CO at extreme low pressures. Tubes prepared in this way and subjected to a mild condensed discharge yielded a spectrum consisting only of the lines and bands of Helium, and a number of new lines which were attributed to Carbon. A notable feature of the latter spectrum was the bright line at λ 5380, recorded previously only as a Carbon line of small intensity. The characteristic spark lines λλ 6583, 6578, 4267, were also absent, or of very doubtful occurrence, and the conditions of excitation led us to suggest that this line spectrum might be the true “arc” spectrum of Carbon, which the energy of the ordinary arc was insufficient to produce, and that of the condensed spark sufficient to repress. Both the line-spectrum and the Comet-Tail bands were investigated only in the visible spectrum; in the present paper observations and measurements of these spectra in the ultra-violet are recorded. In addition, a new band-spectrum apparently associated with the Comet-Tail bands has been measured and expressed by a series formula. The opportunity afforded by the exceptionally strong development of the first negative band-spectrum of Carbon has been taken to re-measure these bands and dispose them in series. Finally, the significance of some of these phenomena is discussed.