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Theoretical prediction of the importance of the 3B2 state in the dynamics of sulfur dioxide

While, the sulfur dioxide molecule has been extensively studied over the last decades, its photoexcitation dynamics is still unclear, due to its complexity, combining conical intersections and spin-orbit coupling between a manifold of states. We present for the first time a comprehensive ab initio study of the intersystem crossing of the molecule in the low energy domain, based on a wave-packet propagation on the manifold of the lowest singlet and triplet states. Furthermore, spin-orbit couplings are evaluated on a geometry-dependent grid, and diabatized along with the different conical intersections. Our results show for the first time the primordial role of the triplet $^3$B$_2$ state which has not been discussed before, giving new insights into the dynamics of the intersystem crossing in $SO_2$.