Temperature- and Pressure-Induced Phase Transitions in p-Difluorobenzene Crystals

The temperature and pressure effects on the Raman-active inter- and intramolecular vibrations of [1H4]- and [2H4]p-difluorobenzene crystals were studied. The observed spectral structure, and the temperature and pressure dependences on the vibrational frequencies of the inter- and intramolecular vibrations indicate the following facts: (1) The temperature-induced phase transitions take place at about 235 and 195 K under 1 atm in [1H4]- and [2H4]p-difluorobenzene crystals. (2) The pressure-induced phase transition takes place under about 2.7 and 2.8 GPa at 298 K in [1H4]- and [2H4]p-difluorobenzene crystals, respectively. (3) A weak C–H···F–C intermolecular interaction exists in crystals.