Hannover 2010 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 12: Photochemistry I

MO 12.7: Vortrag

Mittwoch, 10. März 2010, 12:15–12:30, F 142

Beyond the van der Lugt/Oosterhoff Model: When the Conical Intersection Seam and the Excited State Minimum Energy Path Do Not Cross — •Patrick Kölle¹, Artur Nenov¹, Michael Robb², and Regina de Vivie-Riedle¹ — ¹Ludwig-Maximilians-Universität München, Germany — ²Imperial College London, UK

The photoinduced ring opening reaction of cyclohexadiene is a textbook example for electrocyclic reactions. It was one of the first systems used to elucidate the fundamental role of conical intersections (CoIns) in ultrafast photochemical processes. In this paper we report the complete "minimum energy path" (MEP) in the CoIn space reaching from the closed to the open ring side. The seam was calculated using an analytic approach in which the intersection space in the vicinity of a CoIn is described to second order[1]. The topography of the seam was investigated, revealing minimum energy and transition state structures. In addition the energy profile of the seam was rationalized using valence bond theory. The geometrical changes along the seam have been related to the motions along the excited state MEP in a conceptual model highlighting the quasi parallel orientation of the seam and the IRC-MEP[2]. Our model shows, that even though the van der Lugt and Oosterhoff concept predicts the formation of an avoided crossing along the excited state IRC-MEP, it provides an incomplete description of the decay process to the ground state.

[1] F.Sicilia et al., J. Chem. Theor. and Comp. 4, 257 (2008). [2] A. Nenov, P. Kölle et al., J. Org. Chem., DOI: 10.1021/jo902111r