MRCI calculations of the low-lying electronic states of CuC.

The four electronic states (Σ, Π, Σ, and Π) of CuC corresponding to the lowest dissociation limits Cu( S) + C( P) are calculated by using multi-reference configuration interaction method with Davidson correction (MRCI + Q) approach in combination with the effective core potentials (ECPs) basis sets LANLTZ for the Cu atom and 6-311+g( d) basis sets for the C atom. The calculation covers the internuclear distance ranging from 0.04 to 0.54 nm, and the equilibrium bond length R and the vertical excited energy T are determined directly. The potential energy curves (PECs) show that the lowest two states are the Σ and Π, and Σ is the ground state where the Π state is higher than Σ about 0.28 eV. With the potentials, all of the vibrational levels and rotational constants are predicted by numerically solving the radial Schröbinger equation of nuclear motion. Then the spectroscopic data of ω, ω x, B, and α are obtained after data fitting which are compared with theoretical results currently available. [ABSTRACT FROM AUTHOR]