PHONONS AND ELECTRON-PHONON INTERACTION IN HALOGEN-FULLERENE COMPOUNDS

We have investigated the optical spectra of different halogen-fulleren e compounds: C60I4-x, C70I2, C60Br24, C60Cl24, and C70Cl17. Two types of carbon-halogen bonding have been established: (a) C60I4-x and C70I2 compounds are formed by a C-60 Or C-70 molecule sublattice and an I-2 molecule sublattice that weakly interact via van der Waals forces; (b ) C60Br24, C60Cl24, and C70Cl17 compounds are characterized by covalen t bonds between C and Br/Cl atoms. We have studied in detail the reson ance effects in C60Cl24 using the methods of Raman scattering, infrare d absorption, and absorption in the visible region. The effect origina tes from the interactions between the phonon subsystem and the electro n band at 2.33 eV and manifests itself in a resonant enhancement of th e Raman line intensities and in the repetition of the phonon and the l uminescence spectra shifted by the frequency of Raman-active phonon at 1508 cm(-1). The group-theory analysis of phonon symmetries in rigid and nonrigid C60Br24 and C60Cl24 crystals has been performed.