Structure and Lattice Dynamics of C70 Single Crystals

摘要: Single crystals of C70 are grown from the vapour phase using chro-matographically purified powder as starting material. Most have fcc habit but a minority fraction shows perfect hep morphology. These also microscopically evidenced X-ray and electron diffraction studies. On lowering temperature ideal hcp undergo two transitions due to sequential freezing out rotations molecules around their different axes, resulting in an orientationally ordered low-temperature monoclinic structure. Raman measurements on this structure reveal large number active inter-molecular librational vibrational modes, consistent with selection rules for P21/m-C70. Harmonic lattice dynamics calculations low solid been performed agreement experiments is found. From these additional information orientational ordering obtained observed modes can be quantitatively interpreted.