Pressure-dependent infrared spectroscopy on the fullerene rotor-stator compound C60-C8H8

We carried out infrared transmission measurements of C-60-C8H8 as a function of pressure (0-10 GPa) at room temperature. The kinks in the pressure dependences of the frequencies of the molecular vibrations suggest the occurrence of an orientational ordering transition at around 0.8 GPa. The change in the infrared spectrum indicates symmetry lowering in the high-pressure phase. Furthermore, our data show that the vibrations of C8H8 survive up to a higher pressure than those of C-60, suggesting a shielding of the C8H8 molecules against pressure