Vibrational spectra of several fluorine-substituted allene molecules

The i.r. spectra (200–4000 cm⁻¹) of gaseous and the Raman spectra (0–4000 cm⁻¹) of both gaseous and liquid H₂CCCF₂, HDCCCCF₂, D₂CCCF₂, F₂CCCF₂, H₂CCCHF, FHCCCHF and F₂CCCHF have been recorded and the data interpreted in detail. The normal modes for these molecules have been assigned on the basis of the i.r. band contours, the depolarization ratios, the observed isotopic shifts, and group frequency correlations. Normal coordinate calculations have been carried out for the 1,1-difluoroallene and tetrafluoroallene molecules. For the 1,1-difluoroallene molecule, extensive mixing was found between the symmetric CCC stretch and the symmetric CF₂ stretch whereas less extensive mixing was found for the CF₂ wag with the CCC out-of-plane bend, the CF₂ scissors with the CCC symmetric stretch, and the CCC in-plane bend with the CF₂ rock. For the tetrafluoroallene molecule, extensive mixing was found for the antisymmetric CCC stretch and the out-of-phase symmetric CF₂ stretch.