Temperature- and pressure-induced phase transitions in p-difluoro-benzene crystals

The temperature and pressure effects on the Raman-active inter- and intramo lecular vibrations of [H-1(4)]- and [H-2(4)]p-difluorobenzene crystals were studied. The observed spectral structure, and the temperature and pressure dependences on the vibrational frequencies of the inter- and intramolecula r vibrations indicate the following facts: (1) The temperature-induced phas e transitions take place at about 235 and 195 K under 1 atm in [H-1(4)]- an d [H-2(4)]p-difluorobenzene crystals. (2) The pressure-induced phase transi tion takes place under about 2.7 and 2.8 GPa at 298 K in [H-1(4)]- and [H-2 (4)]p-difluorobenzene crystals, respectively. (3) A weak C-H . . .F-C inter molecular interaction exists in crystals.