Electron--alkali scattering and photodetachment of alkali negative ions

The relation between the scattering of electrons by neutral alkali metal atoms and the photodetachment of the alkali negative ions is discussed, with particular reference to the behavior at the first excitation threshold. Elaborate calculations of the photodetachment cross sections and angular distribution of the electrons ejected in photodetachment of Li-, Na-, and K- are described. Agreement between length and velocity forms and with experiment is good in the case of the first two ions but not as good for K-; it is shown that improved results are obtained if a different model is chosen for the ground state of K-. Structure in the cross sections for these ions is shown to be due to a combination of the effects of a resonance and the threshold behavior. Similar effects in the photodetachment of Rb- and Cs- which take the form of a ''window-type'' resonance just below threshold are described and interpreted. In general, the Wigner threshold law is found to hold only within microvolts of the threshold