Computational perspective on structure, energetics, and bonding of FeC₂O isomers with astrochemical significance

Iron in its elemental form has rarely been detected in the interstellar medium despite being the most abundant refractory element. The presence of iron oxides in the interstellar medium and the recent discovery of FeC in the circumstellar envelope of IRC+10,216 suggest iron-carbon-oxygen molecules as potential interstellar species. In light of this possibility, the potential energy surface of FeC₂O has been investigated computationally using different levels of density functional theory calculations, yielding fourteen, seven, and twenty isomers across the quintet, triplet, and singlet electronic states, respectively. Within the examined DFT frameworks, the lowest energy isomer of FeC₂O is in the quintet electronic state with a linear structure. Single-point (U)CCSD(T) calculations with T₁ diagnostics reveal considerable multireference character in certain geometries. CASSCF optimizations are performed on quintet state geometries to account for the multireference character. Various computational tools, such as adaptive natural density partitioning (AdNDP) analysis, molecular orbital (MO) analysis, and Wiberg Bond Indices (WBI), are employed to elucidate the bonding characteristics of the global minimum geometry. The spectroscopic parameters in both infrared and microwave domains have been successfully computed. The total and the partial density of states are plotted to evaluate how different atoms contribute to the electronic structure. The structural, energetic, and spectroscopic parameters presented in this work have significant implications for future astronomical research.