STRUCTURE AND LATTICE-VIBRATIONS OF CUBIC PENTAERYTHRITOL

In the light of the X-ray investigations by Nitta and Watanabe, Bull C hem soc Jpn 13 (1938) 28, on pentaerythritol a set of equally probable three disordered configurations in the cubic phase has been postulate d. Employing the harmonic rigid molecule approximation of Venkataraman and Sahni, the non-bonded atom-atom interactionpotentials have been o btained by an iterative fit to the lattice energy. Using these potenti als, the long wavelength librational modes have been computed, the eff ect of the disorder on the librational modes of the crystal has been s tudied. The disorder broadens the lattice mode and fluctuates the latt ice energy about a mean position.