Raman Spectrum and Structure of N2F4

The Raman spectra of liquid N₂F₄ at temperatures ranging from −80° to −150°C have been recorded. Depolarization values have been measured. The far‐infrared spectrum of the vapor and solid has also been reinvestigated. Seventeen pronounced Raman lines have been observed whereas the $C_2$ isomer of tetrafluorohydrazine has only 12 fundamentals. The large number of Raman lines suggests the presence of more than one isomer at −120°C. A comparison of the infrared and Raman bands below 800 cm^− 1 shows the mutual exclusion principle is operative and it is concluded from this alternate forbiddeness that the trans‐N₂F₄ isomer of $C_{\text{2h}}$ symmetry gives rise to these mutually exclusive bands. Assignment of the observed frequencies based on depolarization values, band positions, and infrared band contours are presented for the molecule in both the $C_2$ and $C_{\text{2h}}$ configurations. It is shown that the data can only be interpreted in terms of an equilibrium mixture of the two isomers at both ambient and lower temperatures, and that these isomers differ little in energy.