Pressure-Induced Dimerization of C60 at Room Temperature as Revealed by an In Situ Spectroscopy Study Using an Infrared Laser

Using in situ high-pressure Raman spectroscopy and X-ray diffraction, the polymerization and structure evaluation of C-60 were studied up to 16 GPa at room temperature. The use of an 830 nm laser successfully eliminated the photo-polymerization of C-60, which has interfered with the pressure effect in previous studies when a laser with a shorter wavelength was used as excitation. It was found that face-centered cubic (fcc) structured C-60 transformed into simple cubic (sc) C-60 due to the hint of free rotation for the C-60 at 0.3 GPa. The pressure-induced dimerization of C-60 was found to occur at about 3.2 GPa at room temperature. Our results suggest the benefit and importance of the choice of the infrared laser as the excitation laser.