Classical description of the level density and the relaxation behavior of multidimensional molecular curve‐crossing systems

Abstract

AbstractBased on the mapping formulation of nonadiabatic dynamics (Phys. Rev. Lett. 1997, 78, 578), explicit classical expressions for the total level density N(E) of a vibronically coupled molecular system as well as quantum corrections to it are derived. The analytical results for N(E) reveal the relative importance of the various molecular parameters of a curve‐crossing system, such as the electronic bias, the reorganization energy, and the topology of the potential‐energy surfaces. To study the accuracy of the approximate description, numerical studies employing various spin‐boson models as well as a two‐state, three‐mode model of the ultrafast S2 → S1 electronic relaxation in pyrazine are presented. Comparing exact quantum and approximate classical data, the connection between the level density of a vibronically coupled molecular system and its nonadiabatic relaxation behavior is discussed in some detail.