Non-adiabatic coupling of the 11A' and 21A' states of ozone in the vicinity of their conical intersection and construction of diabatic states

The 11A' and 21A' states of ozone are known to have a conical intersection near 830 in C2v, the intersection seam continuing into asymmetric geometries. We have calculated ab initio the symmetric stretch, antisymmetric stretch and bend components of the Born couplings between these states in the vicinity of the intersection seam, using MRD-CI wavefunctions and an analytical gradient formalism. All three components are significant and sharply peaked near the intersection seam. The non-adiabatic couplings in the vicinity of the energetically accessible conical intersection are expected to be important in understanding the spectroscopy of ozone in the region of the Huggins band. The conical nature of the intersection is illustrated. The singularity in the couplings is eliminated by constructing quasidiabatic states. Different diabatization schemes are discussed and compared. The quasidiabatic states are shown to have distinct characteristics.