Quantum coherent dynamics of molecules: A simple scenario for ultrafast photoisomerization - art. no. 040701

We analyze the coherent dynamics of optically excited alkenes in a fully co rrelated 3d tight-binding model with extended Hubbard interactions. The sce nario that emerges is that the steric repulsive interactions are the drivin g force behind ultrafast cis-trans photoisomerizations. This resolves the a pparent discrepancy between values for the torsional stiffness obtained fro m band-structure potentials and from vibrational spectra. The mechanism is illustrated in quantitative detail for ethylene and is also shown to yield a promising scenario for the coherent dynamics of molecules like retinal.