The role of excited state topology in three-body dissociation of sym-triazine

J.D. Savee, V.A. Mozhayskiy, J.E. Mann, A.I. Krylov, and R.E. Continetti
Science 321, 826 (2008)

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.

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