Spin-orbit coupled diabatic potential energy surfaces for quantum dynamics

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Vibronic and relativistic couplings among electronic states are the origin of nonadiabatic effects in molecular dynamics and often have a significant impact on reactions and spectra. Important examples are ultrafast radiationless processes in organic photochemistry, which are induced by conical intersections, or catalytic reactions with transition metals involving spin-forbidden mechanisms. The fundamental understanding and theoretical treatment of such nonadiabatic processes requires the correct handling of such couplings and the determination of fully coupled potential energy surfaces (PESs). The aim of the proposed project is the establishment of a method to generate full-dimensional diabatic PESs including relativistic (e. g. spin-orbit) couplings for medium sized molecules and to apply this new methodology to important benchmark systems. The method will treatall relevant coupling effects with high accuracy and will yield PESs in closed mathematical form to be used in quantum dynamics studies. To this end, our method called Effective Relativistic Coupling by symptotic Representation (ERCAR), which has been developed over the past few years, will be used. So far the method has been applied to the methyl iodide (CH 3 I) system, which has a particularly simple electronic structure within the methyl fragment. Next we want to apply the ERCAR methodology to iodobenzene (C6H5I) which has a more challenging electronic structure in the benzene fragment, presumably leading to new effects in the quantum dynamics. The goal of the proposed project is a thorough theoretical treatment of the photodissociationdynamics of iodobenzene in comparison to experiment and that of methyl iodide.