Infrared spectroscopy on the rotor-stator compounds C60-C8H8 and C70-C8H8 under pressure

Pressure-dependent infrared transmittance measurements on C60–C8H8 and C70–C8H8 were performed at room temperature for pressures up to 10 GPa. The pressure dependence of the vibrational modes suggest the occurrence of orientational ordering transitions induced at 0.5 GPa and 0.8 GPa in C60–C8H8 and C70–C8H8, respectively. In addition, a second anomaly was observed at around 1.3 GPa for C60–C8H8, which could be attributed to the transition to a second, orientationally ordered phase. According to the infrared response, the cubane molecules in C70–C8H8 are more sensitive to the application of pressure compared to C60–C8H8, suggesting larger intermolecular interactions in C70–C8H8