High-pressure Raman spectra of liquid and solid thiophene (C,H,S) have been measured up to 100 kbar at 300 K in a gasketed diamond anvil cell. The pressure dependence of intramolecular and intermolecular vibrational modes revealed a solidification point at 6 kbar and a pressure-induced phase transition at 40 kbar. This solid-solid phase transition was identified as the I11 + IV phase transition by comparison with the intermolecular Raman spectra of the low-temperature solids at atmospheric pressure. The appearance of a dark-red modification of C,H,S, which is irreversibly formed at pressures above 80 kbar with laser irradiation, is discussed.
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