Potential energy surface conical intersection, nonadiabatic coupling

As a last example of a molecular system exhibiting nonadiabatic dynamics caused by a conical intersection, we consider a model that recently has been proposed by Seidner and Domcke to describe ultrafast cis-trans isomerization processes in unsaturated hydrocarbons [172]. Photochemical reactions of this type are known to involve large-amplitode motion on coupled potential-energy surfaces [169], thus representing another stringent test for a mixed quantum-classical description that is complementary to Models 1 and II. A number of theoretical investigations, including quantum wave-packet studies [163, 164, 172], time-resolved pump-probe spectra [164, 181], and various mixed... 

Conical intersections (CIs) between electronic potential energy surfaces play a key mechanistic role in nonadiabatic molecular processes [1 ]. In this case the nuclear and electronic motions can couple and the energy exchange between the electrons and nuclei may become significant. In several important cases like dissociation, proton transfer, isomerization processes of polyatomic molecules or radiationless deactivation of the excited state systems [5,6] the CIs can provide very efficient channels for ultrafast interstate crossing on the femtosecond time scale. 

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