The absorption spectra of mixed metallic vapours

Abstract

It has been known for many years that bands of great complexity occur in the absorption spectra of the alkali metals. The extensive absorption bands of sodium vapour in the green and red portions of the spectrum have, in particular, attracted considerable attention. R. W. Wood has discussed fully the structure of these bands, the manner in which they fluctuate with change in certain physical conditions, and their connection with the fluorescence spectrum. The existence of these bands leads to the conclusion that a certain number of the atoms in an alkali metal vapour are associated, though other considerations have indicated that the proportion present in the molecular form cannot be large. It is reasonable to suppose that, in a mixture of the vapours of two alkali metals, "mixed" molecules containing atoms of both elements will "exist" molecules containing atoms of both elements will exist, in addition to these normally present in the unmixed vapours. These "mixed" molecules if present in sufficient number will exhibit an absorption spectrum, probably similar in character to the bands of the simple alkali metals. In the present communication a new band spectrum is described which is developed only in the vapour of mixtures of sodium and potassium and which, it is suggested, is produced by the sodium-potassium molecules present in the mixed vapour.