On the spectroscopic consequences of different tunnelling mechanisms in non-rigid RPF4 molecules (R = CF3)

Previous experimental results indicate that the CF 3 group in CF 3 PF 4 occupies an equatorial position in the ground state structure and that the less stable axial structure may be reached via a polytopal rearrangement. Such a dynamic behaviour differs drastically from that of CH 3 PF 4 where only permutational rearrangements occur. In the present paper we assume a small distortion of the idealized PF 5 geometry by the CF 3 ligand. In such a case, a description in terms of permutational and polytopal pathways belonging to the same idealized mode is justified. We obtain theoretical modifications of the rotation-vibration spectra of the axial and equatorial configurations of CF 3 PF 4 due to various permutational and polytopal tunnellings. These modifications are characteristic of the pathways and could be used to discriminate between them.