ABINITIO STUDIES OF OPEN-SHELL COMPLEXES OF CO+ WITH RARE-GASES

The open-shell complexes HeCO+, NeCO+, and ArCO+ have been studied using ab initio methods in both the ground and first excited states. Calculations were performed using the 6-311G** and 6-311++G** basis sets with unrestricted Hartree-Fock and Moller-Plesset perturbation theory to fourth order (UMP4). The results predict that all the complexes are bound but that only the Ar species in the ground state is rigid. The most stable equilibrium conformation is linear X-CO+ in the ground state and T-shaped or linear X-OC+ in the first excited state. Observations of these complexes by electronic spectroscopy may be difficult because of the prediction of a geometry change on excitation. The results from several other methods, including restricted open-shell Hartree-Fock with Moller-Plesset, restricted Moller-Plesset for open shells, and quadratic configuration interaction with singles, doubles, and triples, were compared to check that the UMP calculations give a reasonable description of these open-shell molecules.