| Abstract
| - Single crystals of h8-naphthalene have been examined by both X-ray and neutron diffraction over a range oftemperatures from 5 to 295 K. The aim of this case study was to measure the anisotropic displacementparameters (ADPs) of carbons and hydrogens and to interpret them using the model of thermal motion proposedby Bürgi and Capelli (Acta Cryst.2000, A56, 403). The traditional rigid-body analysis expresses the low-frequency motions in terms of molecular translations and librations only, whereas the Bürgi−Capelli treatmentalso includes the high-frequency internal modes. We show that a considerable improvement occurs byrepresenting the internal modes by a single second-rank tensor and that a further improvement follows byincluding a Grüneisen parameter to account for volume thermal expansion. By applying the treatment tomulti-temperature diffraction data, there is a considerable reduction in the ratio of number of adjustableparameters/number of independent observations.
|
