Configuration interaction studies on the electronic states of the CUO molecule

Relativistic multireference configuration interaction calculations are carried out on the low-lying electronic states of the CUO molecule at linear geometries. The results of these and previous CUO calculations are discussed on the basis of the natures of these states and the advantages and disadvantages of different methods of computing electronic structure. We find the (1)Sigma(+)(0) state, at its minimum geometry, to be 0.17 eV lower then the (3)Phi(2) state at its minimum energy geometry. The principal term of the (1)Sigma(+)(0) state is 82.1% of the wave function with no large secondary terms. The principal term of the (3)Phi(2) state is 70.8% of the wave function with a secondary (3)Delta(2) term being 11.6% of the wave function. Calculations on CUO(Ar) at previously optimised geometries give the lowest state as (1)A'.