Photodynamics of polyenes: The effect of electron correlation on potential surfaces

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Abstract
Ground and excited statepotential surfaces for polyenes are calculated by a method that uses an empirical force for sigma electrons and a modified Pariser–Parr–Pople model with configuration interaction through double excitations for the π‐electrons. The effects of electron correlation on the energies, equilibrium geometries, and vibrational frequencies for the ground state and the two lowest excited states (2 1 A g −, 1 1 B u +) of butadiene, hexatriene, and octatetraene are studied and compared with the available experimental data. An analysis of the normal modes of vibration provides an understanding of some of the trends as a func‐ tion of chain length. The model is used also to examine the ground‐state tortional potential in which electron correlation plays an important role.