Rotational Constants. Moments of Inertia. Microwave Spectrum

5 Rotational Constants. Moments of Inertia. Microwave Spectrum 

The trans rotamer of N2F4 is an asymmetric top (x -0.006), its axis of intermediate moment of inertia is the C2 axis. The gauche rotamer approximates a prolate symmetric top (x -0.73) with the C2 axis as the axis of highest moment of inertia. Rotational constants A, B, C and moments of inertia Ia, Ib. Ic obtained from the microwave spectrum and from electron diffraction structural data are given in Table 20. 

6 Molecular Vibrations. Raman and IR Spectra. Force Constants 

For each N2F4 conformer, twelve fundamental vibrations are expected which are distributed among the symmetry species of point groups C2h and C2. They obey the selection rules and exhibit the polarization properties in the Raman spectrum and the types of band contours in the IR spectrum as follows  

The interpretation of the vibrational spectra has been the subject of considerable discussion. A consistent assignment, however, of the fundamental vibrations to the observed Raman and IR bands has not yet been attained, see Table 21, p. 318. 

---