NONADIABATIC COUPLING OF THE 1(1)A' AND 2(1)A' STATES OF OZONE IN THEVICINITY OF THEIR CONICAL INTERSECTION AND CONSTRUCTION OF DIABATIC STATES

The 1(1)A' and 2(1)A' states of ozone are known to have a conical inte rsection near 83 degrees in C-2v, the intersection seam continuing int o asymmetric geometries. We have calculated ab initio the symmetric st retch, 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 c omponents are significant and sharply peaked near the intersection sea m. The non-adiabatic couplings in the vicinity of the energetically ac cessible conical intersection are expected to be important in understa nding 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. Dif ferent diabatization schemes are discussed and compared. The quasidiab atic states are shown to have distinct characteristics.