Adiabatic Potentials for cis-trans Isomerization of Protonated Retinal Schiff-Base with Counter Change

On the protonated retinal Schiff-base interacting with a counter point-charge, the adiabatic potentials of the singlet and triplet states of π-electrons are calculated as functions of the angle θ of rotation about the C 11 -C 12 (double) or the C 10 -C 11 (single) bond, according to our previous formulation and parametrization. It is shown that the cis-trans isomerization around the double bond is characterized by the close approach of adiabatic potentials of the first- and the second-excited singlet state in the vicinity of θ=40° or 140° , not by the crossing between singlet and tirplet states as concluded in the previous two papers. It is also shown that the corresponding eigenfunctions exchange their characters in the small region of approach, and that a similar exchange also occurs at 90° between the ground and the first-excited singlet, although it is not so complete as that at about 40° or 140°.