Conical Intersections and Nuclear Dynamics: A New Look at an Old Problem

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David Yarkony of Johns Hopkins University is supported by the Theoretical and Computational Chemistry Program to study electronically nonadiabatic processes, in which nuclear motion is not restricted to a single Born-Oppenheimer potential energy surface. The role played by conical intersections in nonadiabatic dynamics is a particular focus. The formal and computational tools to develop a fully adiabatic picture of a spin nonconserving, electronically nonadiabatic process for a system with an odd number of electrons will be developed. These tools will be extended to locate and characterize conical intersections with the spin-orbit interaction included in order to treat the most general situation. For the first time, the locus of this type of conical intersection seam will be determined. The reactions of molecular hydrogen with both ground and excited state OH and SH radicals will be investigated to address the effect of increasing spin-orbit coupling. As well, the predissociation of electronically excited OClO, OBrO, and ultimately OIO will be considered. A clearer picture of the relation between the local topography of a conical intersection and the outcome of the nonadiabatic event is expected to emerge from this research. Understanding molecular potential energy surface crossings is crucially important for describing chemical reactions that involve electronically excited states. The task of describing this topic in quantum chemistry its extremely difficult, and likely to be advanced significantly in this project. Successful outcomes will have a major impact on the characterization of chemical reactions initiated by light absorption.