Vibronic spectra, ab initio calculations, and structures of conformationally non-rigid molecules of oxalyl halides in the ground and lowest excited electronic states. Part V: Oxalyl chloridefluoride (COCl-COF)

The structure and conformational dynamics of the COCl-COF molecule in the ground and lowest excited electronic states were investigated theoretically by the CASPT2/cc-pVTZ method. The equilibrium geometric parameters, harmonic vibrational frequencies, potential functions of internal rotation, and adiabatic transition energies were obtained. According to the results of calculations, the molecule in the ground electronic state exist as the trans and gauche (dOCCO ~30-40°) conformers with a low potential barrier to gauche-gauche transition therefore it is impossible to exclude existence of the cis conformer (instead of gauche) with a very broad and flat potential minimum. For all the investigated excited electronic states of oxalyl chloridefluoride molecule calculations predicted the trans and cis conformers. The strong coupling of internal rotation around the C-C bond and non-planar vibrations of carbonyl fragments was found for the excited electronic states. The results of calculation were utilized for reanalysis of experimental ̃{A}^{1} A′ \leftarrow \tilde{X}^{1} A′ and ã {3} A^{\prime \prime} \leftarrow \tilde{X}^{1} A′ vibronic spectra reported in Kidd and King (J Mol Spectrosc 50:209-219 (1974), and ibid. 48:592-599 (1973)). The vibrational assignment that does not contradict the vibrational spectroscopy data and results of calculations was obtained.