Absorption of lithium vapour

Abstract

The fluorescence and channelled absorption spectra of the vapours of the alkali metals have been studied by several physicists, notable among them being Roscoe and Schuster, Liveing and Dewar, Wood and his collaborators, Bevan, and Dunoyer, Wood, working with a concave grating of large radius showed that there are as many as 8,000 absorption lines in the visible region of the absorption spectrum of sodium. In a recent paper Prof. McLennan and Ainslie have given an account of some interesting experiments on the subject, where cesium has been shown for the first time to possess a channelled absorption spectrum in the neighbourhood, and on the short wave-length side, of the first member of the principal series, and a fluorescence spectrum in the near infra-red region. Though attempts were made by these authors to get spectrograms of fluorescence and channelled absorption with the vapour of lithium, no definite results could be obtained, but they pointed out that their preliminary results indicated that lithium possessed a banded absorption spectrum in the ultraviolet region between 0.4 μ and 0.3 μ The failure to obtain channelled absorption spectrum with lithium vapour was probably due to their not obtaining vapour of sufficient density, as the boiling point of the metal is of the order of 1,400°C. In this investigation there were found with lithium vapour not only channelled absorption spectra, both on the short and the long wave-length side of the first line of the principal series, but also, as in the case of sodium, it has been found that there is a fine line absorption spectrum immediately on each side of the main line.