Theoretical study of the TiC molecule: Low-lying and excited 1,3Σ+, 1,3Π, and 1,3Δ states

Highlights: • Theoretical investigation on the electronic states of TiC including recently detected ground & excited states. • The nature of chemical bonding in the ground, low-lying, and excited electronic states are explained. • TiC is held together by a double-π and a half-σ covalent bond in most states with a charge transfer of 0.3–0.5 e^- from Ti to C atoms. • No instances of sp hybridization of C were found in the chemical bonding. We present the results of a theoretical investigation of the TiC molecule, detected recently in experiments. Using state averaged multiconfiguration SCF (MCSCF) followed by multireference configuration-interaction (MRCI) methods, we have calculated relative energies and spectroscopic constants for 14 electronic states of the ^1,3Σ⁺, ^1,3Π, and ^1,3Δ symmetries and analyzed their chemical bonding. Our results are in excellent agreement with the recent experimental findings. Ti and C atoms are held together by $2\frac{1}{2}$ bonds – a double-π and a half-σ, in all the states other than the two ³Π_i states and their singlet analogues. Chemical bonding in the latter is attributed to one π and some σ interactions. There was no instance of sp hybridization of C in the bonding of the excited states. The 4s-4p occupation plays a significant role in the dipole moment and bonding of the electronic states.