PRESSURE-INDUCED PHASE-TRANSITION IN THE 1,2,4,5-TETRABROMOBENZENE CRYSTAL

The effects of pressure on the frequencies and band structures of the Raman active inter- and intramolecular vibrations of the 1,2,4,5-tetrabromobenzene crystal were studied under hydrostatic pressures upto 5 GPa at 300 K in a gasketed diamond anvil cell. Changes of the Raman frequencies and band structures of the inter- and intramolecular vibrations induced by pressure suggest that the phase transition takes place under about 0.7 GPa. Comparison of the pressure-induced frequency shifts of the inter- and intramolecular vibrations of the 1,2,4, 5-tetrabromobenzene crystal with the frequency shifts observed in the 1, 2,4,5-tetrachlorobenzene crystal indicates that the repulsive force between bromine atoms belonging to the adjacent molecules is fairly stronger than the force between chlorine atoms.