Global potential energy surfaces for the lowest two 1A′ states of ozone

Abstract.

The global features of the potential energy surfaces of the lowest two ¹A^′ states of ozone are established and detailed information is determined for the critical regions. Contour maps are generated on a variety of planes and curved surfaces cutting through the two energy surfaces in various directions to obtain a full understanding of the three-dimensional characteristics of both surfaces. Perimetric internal coordinates are used so that the three atoms are treated on an equal footing.

The 1¹A^′ state, the ground state, has a ring minimum and three equivalent open minima, all lying in C ₂-restricted coordinate spaces. Direct dissociation to O₂+O is only possible from the open minima. The lowest energy path from the ring minimum first leads to an open minimum before going to dissociation. The transition states between the ring minimum and the open minima also have C ₂ symmetry. Close to these transition states lie the three open minima of the 2¹A^′ state, which has no ring minimum. Isomerization between the open minima is highly unlikely in the ground state, but not excluded in the excited state. Both states dissociate into the same state of O₂+O, namely the ground state O(³P)+ O₂(³Σ _g ⁻) whose energy lies between that of the 1¹A^′ and 2¹A^′ open minima. There exists an extended, interestingly shaped region in coordinate space in which the two states come very close to each other. It contains an intersection seam between the two states consisting of four branches connected by three knots. Radiationless transitions between the two states can be expected.