Theoretical calculation of transition energies of low-lying electronic states of the CuCl molecule

Ab initio multiconfiguration self-consistent field followed by multireference configuration interaction calculations using localised molecular orbitals were made to estimate adiabatic purely electronic transition energies of the six lowest excited states ( 3 Sigma + , 1 Sigma + , 3 Pi , 1 Pi , 3 Delta , and 1 Delta ) to the X 1 Sigma + ground state of the CuCl molecule. Results show the very strong ionic character of the wavefunctions for all the studied states, di-ionic species having a less important role in the excited states than in CuF, this being especially true for both Pi states. The unobserved X 1 Sigma + from 1 Delta transition is predicted to be found around 26 500 cm -1 . Spectroscopic constants are reported and found to be in good agreement with experimental data for most of the states studied. A comparative analysis of ionicity with CuF is performed through valence, total and orbital electronic densities and a correlated first-order Moller-Plesset Mulliken population analysis for the ground state of both molecules.