The role of excited state topology in three-body dissociation of sym-triazine
Molecular fragmentation into three products poses an analytical challenge to theory and experiment alike. Here we explore the highly debated three-body dissociation of sym-triazine to three HCN products using translational spectroscopy and high-level ab initio calculations. Dissociation was induced by charge exchange between the sym-triazine radical cation and cesium. Calculated state energies and electronic couplings suggest that reduction initially produces a population of sym-triazine partitioned between the 3s Rydberg and n->pi* electronically excited manifolds. Analysis of the topology of these manifolds, along with momentum correlation in the dissociation products, suggests that a conical intersection of two potential energy surfaces in the 3s Rydberg manifold leads to stepwise dissociation, whereas a four-fold glancing intersection in the n->pi* manifold leads to a symmetric concerted reaction.