The electronic structure of the two lowest states of CuC

State-of-the-art ab initio quantum mechanical methods and large basis sets are employed for the study of the electronic structure of the first two states of CuC, (4)Sigma(-) and (2)Pi. A one-electron sigma bond state ((4)Sigma(-)) competes with a two-electron sigma-bond state ((2)Pi) for the ground state of the CuC system. The combined effects of core-valence correlation and relativity point to an X-state of (2)Pi symmetry with D(e)=51.9 kcal/mol and r(e)=1.772 A. The (4)Sigma(-) state is predicted to lie 2.1 kcal/mol higher at r(e)=1.787 A.