Large-amplitude bending vibration in C3 molecule: Refined theory of rovibrational effects supported by ab initio calculations

The present work aims to characterize the diverse spectroscopic properties of an astrophysically relevant C3 homonuclear molecule, with particular attention to its extremely low bending vibration frequency. This ultimately necessitated a refinement of a perturbative Herman–Wallis/Coriolis treatment in which harmonic bending energies and matrix elements are replaced by quantities appropriate to the strongly anharmonic bend. The numerical estimates are obtained through ab initio calculations for the C3 molecule in the electronic ground state. Within the framework of refined theory, we evaluated the Herman–Wallis factors for the ν2 and ν3 bands as well as the ν2l-doubling parameter characterizing the rovibrational interaction. The intensity of the magnetic dipole band ν2 + ν3, which is forbidden in the electric-dipole approximation, was estimated for the first time. We calculated the Raman activity of the symmetric stretching vibration and the polarizability tensor components. The estimated C3 characteristics are compared whenever possible with similar ones for the CO2 molecule.