Theory of Photodetachment near Fine-Structure Thresholds

High-resolution measurements of ${\mathrm{S}}^{-}$ photodetachment near threshold are interpreted on the basis of an intermediate $\left[p^4\right({}_{}{}^3{}_{}{}^{}P)+e(l=0\mathrm{}\left)\right]{}_{}{}^2{}_{}{}^{}P$ complex which dissociates into $\mathrm{jj}$-coupled constituents. The $e-\mathrm{S}$ interaction is represented by doublet and quartet scattering lengths $a_d$ and $a_q$. Relative cross sections are calculated in terms of electron energies, and of $a_d$ and $a_q$. Thereby we generalize to a multichannel process the scattering-length theory of cross sections near $s$-wave thresholds. Many features of the experimental data are accounted for. Predictions are made on the spin-polarization effects of circularly polarized light.