An ab initio study on the structure of the ground state of the C3O2 molecule

Restricted Hartree–Fock and single-reference coupled-pair approximation (SRCPA) calculations were performed for the ground state of the C3O2 molecule. The SRCPA calculations revealed that C3O2 is quasi-linear with a global minimum in a W-shaped structure (C2v symmetry) with ∠C–C–C=153.6° and ∠C–C–O=176.4°. The observed very low frequency of 18.2 cm−1 is not a fundamental vibrational frequency along the ν7 mode, but should rather be assigned to the transition between two vibrational states which are split by the interaction of two ground vibrational states in the double minima.