Where is the unpaired electron in the phosphoranyl radicals H₃PS^- and H₃PSH?

High-level, correlated electronic structure calculations on H₃PS^- and H₃PSH indicate these two radicals to adopt trigonal bipyramidal geometries in which the unpaired electron is localized equatorially, although for the neutral species only the equatorially oriented mercaptan is stable to PS bond homolysis. The two radicals are otherwise fairly similar in both structure and predicted isotropic hyperfine splittings. Moreover, stereomutations on the H₃PSH hypersurface are analogous to those predicted for H₃POH.