Raman scattering in non-polymerized and photo-polymerized C60 films at 5 K

Abstract

The Raman spectra of non-polymerized and photo-polymerized fullerene films of various polymerization degrees were studied at 5 K in the 250–1590 cm−1 range. It was found that the Raman spectra of non-polymerized film display splitting of the lines corresponding to Ag and Hg vibrational modes of free C60 molecule which is induced by the crystal field of the low-temperature phase. The Raman spectra of photo-polymerized films at low temperatures exhibit pronounced lines corresponding to Ag(2) vibrations of monomers, dimers and linear chains. Based on the analysis of the spectra of photo-polymerized films of various polymerization degrees (∼45, ∼85, and ∼95%), the spectrum evolution in the region of molecular modes of fullerene was studied vs. polymerization degree. It was found that in the films with high polymerization degree (∼85 and ∼95%), the linear polymer chains dominate while in the film with lower polymerization degree (∼45%) the dimers are dominant. An increase of polymerization degree entails a significant frequency increase (∼2.8 cm−1) of Ag(2) mode of the fullerene monomer induced by changes in its environment upon the transition from non-polymerized to photo-polymerized films. Such a shift was not observed for the lines corresponding to the fullerene photopolymer.