High‐pressure Raman study of liquid and solid thiophene up to 100 kbar at 300 K

Abstract

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.

Molecules under extreme conditions: Chemical reactions at high pressure

“…Also in this case the reaction is extremely sensitive to photochemical effects as previously reported by Shimizu and Matsunami in a high pressure Raman experiment. 114 Thiophene was observed to transform into a dark red material above 8 GPa when irradiated with 50 mW of the 514.5 nm Ar + laser line. In contrast, the reaction was not observed without irradiation.…”

Evidence for Orientational Order in Nanothreads Derived from Thiophene

“…In situ vibrational spectroscopy is consistent with the diffraction results. Characteristic Raman modes of Phase III include intermolecular phonons (100−200 cm −1 ), ring bending (450−760 cm −1 ), ring stretching (830 cm −1 , 1350− 1430 cm −1 ), C−H bending (1000−1100 cm −1 ), and C−H stretching (3000−3100 cm −1 ), 47,48 all increasing in frequency with pressure. Around 5.5 GPa, we observed four new lattice modes between 70 and 160 cm −1 , four new modes in the C−H bending region from 1070−1120 cm −1 , and two new modes in the C−H stretching region from 3130−3140 cm −1 (Figure 2a−d); these new peaks share similarities with low-temperature Raman spectra of Phase IV, or could indicate a sluggish transformation to Phase V. 47,49 Above ∼6.1 GPa, the broad lattice modes split into multiple sharp peaks, closely resembling the changes observed in the low-temperature sequence from Phases III to IV to V. 49 Mode splitting with increasing pressure is attributed to a decrease in orientational disorder, i.e., more distinguishable local environments: Phase III is disordered, while Phase V is ordered.…”