The spin-orbit coupling in the bond formation region of the electronic ground states of O3+, S3+ and SO2+

The potential energy surfaces and the spin-orbit couplings for all states correlating with the lowest dissociation asymptotes 2Π + 3P of the radical cations of ozone, thiozone and sulfur dioxyde have been calculated in the asymptotic and bond forming regions employing full valence CASSCF wavefunctions. For linear geometries, the 2Π and 4Π states are calculated to be nearly degenerate for distances corresponding to about twice the Re distance of their equilibrium ground state values. Their attractive potentials are distinctly lower than those of the other states. The spin-orbit mixing renders their assignments by spin quantum numbers impossible. This implies that, for instance, the analysis of the observed O3+ rotationally resolved spectra near the dissociation threshold must include not only the vibronic couplings between the X∼2A1 and A∼2B2 states but also very complex angular momentum interactions. Similar behavior is found also for the 2Π and 4Π states resulting from the lowest asymptote in the S3+ and SO2+ radical cations.