RAMAN-STUDY OF THE POLYMERIZED STATE OF RBC60 AND CSC60

We report a room-temperature Raman investigation of C-60 and orthoromb ic AC(60) phase (o-AC(60)). The o-AC(60) phase is present when the sam ple is slowly cooled from the AC(60) fee disordered phase (T > T-c of about 370 K) to room temperature. In the o-AC(60) phases large changes in the intensity of intramolecular modes not active in C-60 as well a s splitting of some modes of C-60 are observed. In addition, new modes at 342, 632, and 967 cm(-1) are evidenced. Nevertheless, from these d ata the length and the geometry of the oligomers phase cannot be unamb iguously defined. Only the significant differences between the o-AC(60 ) Raman spectrum and the Raman spectrum of photopolymerized C-60 and p ressure-induced polymerized phases of C-60 indicate some differences i n the structural organization of C-60 monomers in the o-AC(60) phase w ith respect to these systems. In both o-RbC60 and o-CsC60 phases the l ow-frequency Raman spectrum as excited at 776 nm exhibits a well-defin ed peak at around 31 cm(-1). The assignment of this mode is discussed and we propose to attribute it to the interball stretching mode in the relatively long oligomer (longer than dimer). This assignment support s the mechanism of polymerization via a (2+2) cycloaddition reaction b etween C-60 molecules in the o-AC(60) phase.