The X 3   and a 1  electronic states of neutral SO are accessed at 532 and 611 nm, with an additional b 1   state also visible at 355 nm. The vibrational assignments (𝑣′,𝑣″) for the dominant peaks in the spectra are indicated in Fig. for the SO(X 3 Σ  , a 1 , b 1 Σ  ; 𝑣′)  SO  (X 2 3/2; 𝑣) transitions from the = 3/2 spin-orbit component of the anion electronic state. The PADs obtained from the Abel-inverted images were analyzed to determine the anisotropy of each transition. The values of the anisotropy parameter  for each spectral peak were obtained by fitting the standard one-photon PAD function 𝐼 𝜃 𝜎/4𝜋 1 𝛽𝑃 cos 𝜃