Ab initio calculations, of the ground and low-lying electronic states of O-4 along the minimum energy paths (MEP) for the reactions O-2(X (3)Sigma(g)(-))+O-2(X (3)Sigma(g)(-))-->O-4(X (1)A(1)) and O-2(X (3)Sigma(g)(-))+O-2(X (3)Sigma(g)(-))-->O-3(X (1)A(1))+O(P-3) have been performed. Our CASSCF(16,12)+CASMP2 calculations using the 5s4p3d2 f ANO basis set provide a solid basis to establish the stability of the O-4 chemically bound molecule. Surface crossings between singlet and triplet states have been found and further characterized by evaluating their spin-orbit coupling matrix elements. Our calculations show that for the ozone formation reaction there should be spin-orbit coupling transitions allowing vibrational to electronic energy transfer around the saddle point region. The formation of vibrationally excited O-2(a (1)Delta(g),v) is predicted to contribute to the dark channel reported in experiments.