Photodetachment of Li¯ and Na¯

Reliable estimates of the photodetachment cross sections and electron affinities of the negative ions of the alkali metals are required for interpretation of the properties of low-temperature plasmas, and in the fields of upper-atmosphere physics and astrophysics. Experimental data are rather scarce and uncertain, the electron affinities being too low (∿0.5 eV) for application of standard photoabsorption techniques near threshold. Even if this were possible, the cross section is expected to display a k3 dependence at threshold appropriate to an s \textrightarrow p transition, thereby precluding a sharp onset. The electron affinity of lithium has been measured by Ya akobi,1 in experiments with electrically exploded lithium wires, and by Sheer and Fine,2 who studied the positive and negative surface ionization of a lithium beam. Two measurements of the electron affinity of sodium and the heavier alkali metals using resonant charge exchange are cited in the review of Smirnov.3 No measurements of the photodetachment cross sections have been made.