Raman and mid-infrared spectroscopic study of the phase transitions in octafluoronaphthalene at elevated pressures

Raman and mid-infrared spectra of C₁₀F₈ have been obtained under hydrostatic pressures up to 17 kbar in a diamond anvil cell. The C₁₀F₈ I–II phase change, previously observed by neutron diffraction at about 0.8 kbar, has been confirmed. No evidence was found to support the existence of a furtt ier phase change between 4 and 6 kbar indicated by the neutron work, although this is certainly not precluded as the extra spectral features expected in this case are extremely small. The mode Grüneisen parameters, γ_i, allow a clear distinction between internal and external molecular modes, and scale roughly in accord with Zallen's relation γ_i$\text{\$}\text{?}$v_i^?2.