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

Abstract

Ground and excited state potential 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 1Ag−, 1 1Bu+) 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.