FIG. 1.

Contour plots near the conical intersection: (a) the 1¹A₁ state potential energy surface; (b) the 2¹A₁ state potential energy surface; (c) the energy difference E(2¹A₁) − E(1¹A₁). The energies were obtained from state-averaged CASSCF(18,12)/cc-pVQZ calculations and are given in mh. In panels (a) and (b), the energies given for the contours are with respect to the energy of the 1¹A₁ state at the open minimum. The coordinates p and q of panel (c) are indicated in panels (a) and (b) by green vectors. The range of panel (c) is indicated in (a) and (b) by the dashed green boxes. Note the difference in the scales of the coordinates and the energies. The red, blue, and black asterisk-like symbols identify the positions of the TS, the XM, and the CI, respectively.