The spectral assignments and spectroscopic constants of SO  and the three lowest electronic states of SO have been reported previously. In this work, we focus on the information contained in the photoelectron angular distributions. In particular, we highlight the differences between two isovalent anions, SO  and O2  . O2  PADs have been studied in detail previously. For easy comparison with the present SO  data, Fig. (b) displays the anisotropy values for the X 3 Σg   X 2 g transition in O2  , similarly plotted with respect to eKE. The O2   values were reported previously by Van