Infrared study of vibrational property and polymerization of fullerene C60 and C70 under pressure

Abstract

Infrared spectra were measured for solid C60 and C70 to 7 GPa under hydrostatic or quasi-hydrostatic pressure at room temperature. Some vibrational modes showed negative or insensitive dependence of frequency on pressure, suggesting destabilization of C60 and C70 molecules by compression. In solid C60 new absorption bands gradually grew with increasing pressure in association with an intensity decrease of the original bands. These spectral changes were interpreted in terms of polymerization of C60 molecules. Polymerized molecules recovered at ambient pressure were converted back to the monomer by thermal annealing at 473 K.