Highly correlated ab initio methods were used in order to generate the potential-energy curves of the SO+ electronic states correlating to S+(S-4(u))+O(P-3(g)) and S+(D-2(u))+O(P-3(g)). These curves were used for deducing accurate spectroscopic properties for these electronic states. Our calculations predict the existence of a (2)Phi state lying close in energy to the well-characterized b (4)Sigma(-) state and several weakly bound quartet and doublet states located in the 6-9 eV internal energy range not identified yet. The spin-orbit integrals between these electronic states were evaluated using these highly correlated wave functions, allowing the discussion of the metastability and the predissociation processes forming S++O in their electronic ground states. Multistep spin-orbit-induced predissociation pathways are suggested. More specifically, the experimentally determined dissociative potential-energy curve [H. Bissantz , Z. Phys. D 22, 727 (1992)] proposed to explain the rapid SO+(b (4)Sigma(-),v >= 13)-> S+(S-4(u))+O(P-3(g)) reaction is found to coincide with the 2 (4)Pi potential-energy curve for short internuclear distances and with the repulsive 1 (6)Pi state for longer internuclear separations. (c) 2006 American Institute of Physics.