The vibrational spectra of perfluoro- and perchlorobutatriene

Raman data are reported for gas, liquid and solid perfluorobutatriene, F₂CCCCF₂, and infrared data for gas and solid. They show clearly that the molecule has the expected planar structure of D_2h symmetry. With the aid of Raman depolarization ratios and infrared band contours, twelve of the seventeen spectroscopically-active fundamentals can be assigned with assurance. Frequencies are suggested for the remaining five modes.Data for perchlorobutatriene are limited to the solid state except for some depolarization measurements in solution. Again only D_2h symmetry is acceptable. About half the fundamentals can be assigned with confidence.