Intersecting conical intersection seams in tetra-atomic molecules: the S1–S0 internal conversion in HNCO

Abstract

Symmetry-allowed intersections of two states of different symmetry, different-symmetry intersections, are the class of conical intersection most commonly studied in small molecules. A same-symmetry seam of conical interaction, originating from the same two states, may intersect this different-symmetry seam. These intersections of intersections are themselves continuously connected, forming a multidimensional subspace in the symmetry-allowed seam. A confluence of seams requires changes in the conical topography which can affect nuclear dynamics significantly. The indirect photodissociation of HNCO to H + NCO results from an internal conversion attributable to the portion of the S0-S1 seam with HNCO in a trans configuration. A previously introduced perturbative analysis is used to show that a manifold of confluences of conical intersections exists in this region. These confluences can influence the internal conversion dynamics and should be incorporated into a detailed description of this process. This represents the first time a dynamically relevant manifold of confluences has been demonstrated in a tetra-atomic molecule.