Photodetachment spectroscopy near the lowest threshold of the S$^{-}$ ion

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