Infrared and Raman Spectra of Fluorinated Ethanes. XII. 1,1,2,2-Tetrafluoroethane

The infrared absorption spectra of gaseous CHF2–CHF2 at five temperatures between 30° and 170°C and of the crystalline solid at —170°C have been obtained with a Perkin-Elmer double-pass spectrometer equipped with CsBr, NaCl, and LiF prisms. The Raman spectrum of the liquid at 20°, —25°, and —80°C has been photographed with a 3-prism glass spectrograph of reciprocal linear dispersion 15 A/mm at 4358 A, and polarization measurements have been made. In the gaseous and liquid states the compound exists as a mixture of two rotational isomers of symmetries C2h and C2, respectively, the former (trans) being the more stable. In the crystalline state only the trans configuration is present. A value of 1160±100 cal/mole was found for the enthalpy difference ΔH0 in the gas. In the liquid ΔH0 is much smaller. With some uncertainties, the vibrational fundamentals have been assigned for each isomer.