Electronic Structure and Bonding Nature of the Ground State Monocarbide Cations, ScC+, TiC+, VC+, and CrC+

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Abstract
The ground states of the transition-metal diatomic carbide cations, MC+ (M = Sc, Ti, V, and Cr), are studied using multireference configuration interaction (MRCI) methods in conjunction with quantitative basis sets. Full potential energy curves are calculated for all four systems. When 3s23p6 core/valence correlation contributions and scalar relativistic effects are taken into account, our best estimates for the zero-point-corrected dissociation energies of the MC+ series are in good agreement with relevant experimental results. For TiC+, the recent correlation-consistent-type basis sets for Ti of Bauschlicher are also exploited to extract complete basis set limits of selected properties. The ground states of VC+(X 3∆) and CrC+(X 2∆) are reported for the first time in the literature. For CrC+ an interesting competition is revealed between the 2∆ and 4Σ- states; although 4Σ- is formally the ground state at the MRCI level of theory, when core/valence and/or relativistic effects are included, the ground state of CrC+ becomes of 2∆ symmetry, with a calculated energy separation (a 4Σ- ← X 2∆) of 2.3 kcal/mol.