On the ground and excited electronic states of LaCO and AcCO

High-level ab initio electronic structure analysis of correlated lanthanide- and actinide-based species is laborious to perform and consequently limited in the literature. In the present work, the ground and electronically excited states of LaCO and AcCO molecules were explored utilizing the multireference configuration interaction (MRCI), Davidson corrected MRCI (MRCI+Q), and coupled cluster singles doubles and perturbative triples [CCSD(T)] quantum chemical tools conjoined with correlation consistent triple-zeta and quadruple-zeta quality all-electron Douglas-Kroll (DK) basis sets. The full potential energy curves (PECs), dissociation energies (Des), excitation energies (Tes), bond lengths (res), harmonic vibrational frequencies (omega es), and chemical bonding patterns of low-lying electronic states of LaCO and AcCO are introduced. The ground electronic state of LaCO is a 4 Sigma- (1 sigma 11 pi 2) which is a product of the reaction between excited La(4F) versus CO(X1 Sigma+), whereas the ground state of AcCO is a 12 Pi (1 sigma 21 pi 1) deriving from ground state fragments Ac(2D) + CO(X1 Sigma+). The spin-orbit ground states of LaCO (14 Sigma-3/2) and AcCO (12 Pi 1/2) bear similar to 13 and 5 kcal mol-1D0 values, respectively. At the MRCI level, the spin-orbit curves, the spin-orbit mixing, and the Tes of spin-orbit states of LaCO and AcCO were also analyzed. Lastly, the density functional theory (DFT) calculations were performed applying 16 exchange-correlation functionals that span three rungs of "Jacob's ladder" of density functional approximations (DFAs) to assess DFT errors associated on the De and ionization energy (IE) of LaCO.