Hexamethylenetetramine: extinction and thermal vibrations from neutron diffraction at six temperatures

摘要: Neutron diffraction data have been collected for hexamethylenetetramine (HMT) at 15, 50, 80, 120, 160 and 200K using a single crystal (mass 8.1 mg). The structure refinement each temperature included two extinction parameters third-order thermal the H nuclei. Extinction effects are very severe with factors as small 0.2Fkin2 three reflections (800, 110 440). Application of Sabine theory indicates that domain size decreases from 115 microns 200 K to 85 15 K. half-width in mosaic spread (7" arc) is almost independent temperature. An model without phase correlations between blocks gives slightly better fit data. nuclear mean square displacements analysed assuming no coupling external (rigid body) internal vibrations. This rigid-body vibration which zero-point vibrational apparent. methylene nuclei vibrations approximately At K, anharmonic component, but temperatures below this becomes insignificant terms experimental error.