LATTICE-DYNAMICS OF PENTAERYTHRITOL

Employing the external mode formalism of Venkataraman and Sahni, Rev M od Phys, 42 (197 409, for complex crystals, the lattice dynamics of te tragonal pentaerythritol is worked out. The non bonded atom-atom inter action potentials are obtained by an iterative fit to the lattice ener gy and equilibrium conditions. The long wavelength librational modes o btained with these parameters are in good agreement with the IR and Ra man data on PET and its deuterated analogues. The potential parameters confirm the influence of strong hydrogen bonding and layer structure of the crystal on the degenerate and the non-degenerate librational mo des in the xy-plane and z-direction respectively.