Ab initiostudy of NO2

Abstract
We report ab initio MRD-CI calculations for the two lowest 2A′ states ([Xtilde]2A1 and à 2B2) of the NO2 molecule. A diabatic representation has been obtained by transforming the adiabatic CI wavefunctions in such a way that the resulting states have equal diagonal terms for the dipole moments perpendicular to the bisector of the bond angle. The method is tested for three different cross-sections of the potential-energy surfaces and is found to yield the desired small and constant coupling elements in the diabatic basis, even in the region of the conical intersection itself.