Photodetachment from the S$^{-}$ ion at the $^{2}$P$_{1/2 }\to $ $^{3}$P$_{2}$ threshold

Numerous experiments have investigated photodetachment spectroscopy in a magnetic field at the $^{2}$P$_{3/2 }\to \quad ^{3}$P$_{2}$ threshold of ions such as S$^{-}$ and O$^{-}$. The energy of this threshold is known as the atom's \textit{electron affinity}. In this work we have investigated detachment at the lowest-lying threshold for the S$^{-}$ ion, the $^{2}$P$_{1/2 }\to \quad ^{3}$P$_{2}$ threshold. Our experimental apparatus includes a Penning ion trap in which the ions are created, trapped and stored, and a single-mode, ring dye laser. Our observations yield a quantitative measurement for the threshold energy and an indirect measurement for the spin-orbit splitting of the S$^{-}$ ion.