Journal of the American Chemical Society, Vol.125, No.9, 2804-2808, 2003
Relationship between photoisomerization path and intersection space in a retinal chromophore model
A low-lying segment of the intersection space (IS) between the excited-state and the groundstate energy surfaces of a retinal chromophore model has been mapped using ab initio CASSCF computations. Analysis of the structural relationship between the computed IS cross-section and the excited state Z --> E isomerization path shows that these are remarkably close both in energy and in structure. Indeed, the IS segment and the Z --> E path remain roughly parallel and merge only when the double bond reaches a 70degrees twisting. This finding supports the idea that, in certain chromophores, a more extended segment of IS, and not a single conical intersection, contributes to the decay to the ground state.