The potential energy surfaces (PESs) and the spin-orbit couplings for all states of sulfur dioxide correlating with the lowest O((3)p) + SO(X(3)Sigma(-)) asymptote have been calculated in the bond formation region employing correlated electronic wavefunctions. The PESs are found to be strongly anisotropic along the bending coordinate. For linear (OSO)-O-... approach, the Sigma states lie below the Pi states; for the (OOS)-O-... orientation the Pi/Sigma ordering is opposite. For perpendicular approaches their A' components form avoided crossings. The electron spin quantum number is no longer a good quantum number for geometries where the multiplets come close together. (c) 2005 Elsevier B.V. All rights reserved.