Electron affinities of Cu and Ag

In a crossed‐beam experiment, photodetachment of Cu⁻ and Ag⁻ ions by an Ar‐ion laser beam (4880 Å) is studied by energy analyzing the detached electrons. The electron affinities are found to be: E.A. $(\mathrm{Cu}\text{)=(1.226 ± 0.010)\hspace{0.17em}}\mathrm{eV,\; E.A.}\mathrm{\hspace{0.17em}(}\mathrm{Ag}{\text{)=(1.303}}_{\text{−0.011}}^{\text{+0.007}}\mathrm{)\hspace{0.17em}}\mathrm{eV}$ . These electron affinities are approximately 0.5 eV less than those determined by surface ionization studies. The surface ionization technique is discussed and possible reasons for the discrepancies are advanced. The new electron affinities are used to estimate those of the atoms in the long series of the periodic table. Measurements of the angular distribution of the photodetached electrons yield $\text{β=2.00 ± 0.03}$ for the anisotropy parameter β in both cases.