The phase transition in octafluoronaphthalene has been investigated by Raman scattering and neutron powder diffraction. The weight of the experimental evidence points to a unit cell doubling in the a direction, but with no change in space group symmetry. Lattice dynamics calculations support this evidence and indicate that the mechanism of the phase transition may well be the instability of a zone boundary acoustic mode of librational character. The structure of the low-temperature phase has been refined and the Raman spectra of the upper and lower phases are reported.
Mackenzie, G. A., Arthur, J. W., & Pawley, G. S. (1977). The Structural Phase Transition in Octaflournaphtalene. Journal of Physics C: Solid State Physics, 10(8), 1133-1149. https://doi.org/10.1088/0022-3719/10/8/016