Lattice vibrations in crystallineC70

Raman spectroscopy in single-crystalline ${\mathrm{C}}_{70}$ at low temperatures reveals a large number of Raman-active intramolecular modes, consistent with the selection rules and in agreement with theoretical predictions. Librational and vibrational lattice modes are observed in the low-frequency region of the spectrum, consistent with the selection rules for monoclinic P${112}_1$/m-${\mathrm{C}}_{70}$. We discuss the lattice modes in terms of a simplified model of the crystal potential. Near 280 K we observe a phase transition, which is assigned to the order-disorder transition for the rotational motion around the long molecular axis.