Continuous absorption of light in sodium vapour.

Abstract

THE continuous absorption of light in sodium vapour, corresponding to the photo-ionization of the atom, has been measured with an apparatus generally similar to that used by Ditchburn, Tunstead and Yates1 for potassium vapour. Under the conditions of the present experiment, the absorption due to molecules is small compared with that due to atoms at the series-limit (2411 A.). After correcting for the molecular absorption, the atomic absorption coefficient at the series-limit (σl) is found to be 1.16 × 10−19 cm.2. This value is subject to an error of ± 10 percent, about half of which is due to uncertainty in the vapour pressure2. The variation of absorption coefficient with wave-length is shown in the accompanying graph, σλ/σl being plotted as a function of λ down to 2150 A. The accuracy of photometry decreases rapidly as the wave-length decreases beyond this point, and we can only state that the absorption lies between the two dotted curves. It appears probable that there is a minimum in the absorption curve at, or near, 2150 A.; but this cannot be stated with certainty.