Photochemical reactions conical intersection, computational model

Fig. 2. The relationship between (a) the Van der Lugt-Oosterhoff model and (b) a model (see Sec. 2.1) based on MEP computations for the photochemical electrocycliza-tion of buta-1,3-diene. The Van der Lugt-Oosterhoff model is based on an assumed (interpolated) reaction coordinate and suggests that the photochemical funnel corresponds to an avoided crossing at M (see dashed frame). MEP computations yield a different, but unbiased coordinate, corresponding to the steepest-descent path from the excited-state reactant. The reaction coordinate characterizing such a path leads to a conical intersection between the excited (5i) and ground (So) states. The framed region in part (b) indicates the position of the Van der Lugt-Oosterhoff avoided crossing in the conical intersection region.

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