The Role of Excited-State Topology in Three-Body Dissociation of sym -Triazine

Abstract

Molecular fragmentation into three products poses an analytical challenge to theory and experiment alike. We used translational spectroscopy and high-level ab initio calculations to explore the highly debated three-body dissociation of sym -triazine to three hydrogen cyanide molecules. 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 π* ← n 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 π* ← n manifold leads to a symmetric concerted reaction.