INFRARED AND RAMAN STUDIES OF PRESSURE-POLYMERIZED C-60

We discuss the room-temperature infrared and Raman spectra for the pre ssure-induced rhombohedral, tetragonal, orthorhombic C-60 polymers and the C-60 photopolymer. The interfullerene bonds are found to not only split the H-1g- and F-1u-derived modes, but also to soften these intr amolecular modes relative to those in pristine solid C-60 The observed mode softening is attributed to the loss of C=C bonds in the molecula r cages, which are broken to reform as intermolecular four-membered ri ngs. Lorentzian line-shape analysis of the Raman data in the vicinity of the pentagonal pinch mode frequency in these polymerized structures reveals six distinct Raman lines at very nearly the same frequencies. However, the relative intensities of these lines were found to be sen sitive to the phase of the fullerene polymers. The frequency of the A( g)(2)- and the F-1u(4)-derived modes is found to depend linearly on th e intermolecular coordinate al of the polymeric phases; A frequency so ftening of Delta omega/Delta a(I) similar to 19 and 58 cm(-1)/Angstrom was deduced for the Ag(2)- and the F-1u(4)-derived modes, respectivel y. In addition, the experimental spectra are compared to the vibration al spectra obtained from a first-principles molecular dynamical calcul ation for a C-60 dimer and an infinite chain of polymerized C-60.