Vibrational spectroscopy at high pressures in CF4: Implications to the phase diagram

The molecular analogue of methane. CF4 is the most fundamental saturated pe rfluorocarbon, exhibiting complex optical behavior that is highly unusual f or such a simple molecular system. We present Raman measurements in solid C F4 over a wide range in pressure from 1.6 to over 30 GPa at room temperatur e. The Raman spectra exhibit polarization-dependent intensity variations an d history-dependent absence or presence of high pressure modes. Our results compellingly demonstrate that previously identified phase transitions in C F4 based on Raman signatures need to be reconsidered. Though our data sugge st possible new high-pressure transitions, we do not identify new phases be cause of spectral complexity. Finally, we used the measured longitudinal an d transverse optical mode splitting to estimate the dipole moment derivativ e at high pressures and find it close to that of gaseous CF4.