LATTICE DYNAMICAL STUDY OF A INTERNAL CHARGE-TRANSFER MOLECULAR-CRYSTAL - 4-NITROPYRIDINE N-OXIDE AND ITS DEUTERATED DERIVATIVE

Phonon dispersion curves, far-IR and low-frequency Raman spectra (belo w 200 cm-1) of 4-nitropyridine N-oxide (NPO) including results at high pressure and low temperature are reported and interpreted with the he lp of a lattice-dynamical calculation using atom-atom Buckingham-type potentials and a multipole expansion up to the quadrupole. The charge transfer process is analysed through its manifestations on the model p arameters of some short intermolecular interactions. The good agreemen t between calculation and experience is confirmed by using the same mo del to interpret the experimental results of inelastic neutron scatter ing along the b direction of a deuterated NPO-d4 single crystal.