Abstract
OPTICAL spectra present two main types of regularity, line series and band series. The two are very different in appearance: the line series is seldom recognisable by inspection, for it comprises as a rule comparatively few lines, the strongest of which are widely separated and usually confused with other lines; whilst band series are among the most striking and beautiful of spectral phenomena, containing large numbers of lines crowding together to so-called “heads “in the most obviously orderly manner. Their arrangement may be described by associating successive integers m with successive lines, when their wave-numbers are found to be given, to a near approximation, by an expression of the form A + Bm + Cm2, where A, B, C are constants. Moreover, a law of the same general type was found by Deslandres to connect the wave-numbers of heads of associated bands when these occur in groups, as is commonly the case. Finally, there may be a number of these groups of heads constituting what may be called a system of bands, and these again are distributed in much the same way as the heads within a group or the lines associated with a head. A system of bands is thus a very complex affair, containing, it may be, some thousands of lines and requiring much labour and powerful instrumental means for its complete analysis. Nevertheless, fairly comprehensive data have now been accumulated for the more intense band systems lying in the visible and near ultra-violet regions of the spectrum, and these offer a rich field of investigation to the theoretical physicist. It is proposed in this article to indicate in the broadest outline the present position with regard to the theoretical interpretation of band spectra.
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The Quantum Theory of Band Spectra. Nature 113, 874–875 (1924). https://doi.org/10.1038/113874a0
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DOI: https://doi.org/10.1038/113874a0