The photoionization absorption continua for alkali metal vapours

Abstract

Absorption measurements are reported for the metal vapours potassium, rubidium and caesium and existing data for lithium and sodium are reviewed. The separation of atomic and molecular absorption is discussed and the data presented as absolute cross-section curves as a function of wavelength. The shapes of the atomic photoionization continua and their absolute values are discussed in relation to existing theoretical cross-sections data. Best experimental values of the cross-sections at the series limits are found to be : Li = 1.9 ± 0.2 Mb, Na = 0.125 ± 0.01 Mb, K = 0.007 ± 0.002 Mb, Rb = 0.10 ± 0.015 Mb and Cs = 0.20 ± 0.03 Mb. The curves for potassium, rubidium and caesium have non-zero minima and that for sodium has a minimum which is near zero. Experimental minimum values of 4 ± 2 x 10 -3 Mb, 8 ± 3 x 10 -3 Mb and 6 ± 1 x 10 -2 Mb for potassium, rubidium and caesium respectively are obtained.