To apply this approach to SO  , the anion geometry was optimized with CCSD(T)/aug-cc-pVTZ. The equation-of-motion (EOM-CCSD) method was then used to calculate the Dyson orbitals for each of the SO(X 3 Σ  , a 1 , b 1 Σ  )  SO  (X 2 3/2) transitions at the optimized geometry (R = 1.592 Å) of the anion. Two different EOM approaches were used. In the first, the SO  (X 2 3/2) and SO(X 3 Σ  , a 1 , b 1 Σ  ) states were obtained using electron-attachment (EOM-EA-CCSD) and spin-flip (EOM-SF-CCSD) calculations, respectively, starting from the common triplet-state CCSD reference. This approach uses a well-behaved reference and treats the initial (SO  ) and all the final (neutral SO) states on an equal footing. The second approach uses ionizationpotential (EOM-IP-CCSD) ansatz to access each of the three neutral states starting from the (doublet) anion reference. By virtue of using orbitals and coupled-cluster amplitudes optimized for the anion, this approach describes the anion state better than the first one, but can be affected by artifacts due to symmetry breaking of the open-shell doublet reference and an imbalance in treating degenerate π * orbitals.