Abstract
Symmetrized multipole formalism, in
diffraction studies of orientationally disordered molecular crystals, is
generalized to include coupling between orientations and translations
of a rigid body and anharmonicity in the center-of-mass motion. This
generalized formalism is intended for use with direct multipole analysis
of the observed form factors. In the relationships between the radial
multipole coefficients of the dynamic and static density, correlations
cause a mixing in the multipole order. In the dynamic form factor the
parameters describing the coupling are linear combinations of the
multipole expansion coefficients of the corresponding rigid-body
distribution. Parameters describing anisotropy are directly the
multipole expansion coefficients of the rigid-body center-of-mass
distribution. As an example of the formalism, neutron diffraction data
from cubic KCN, NaCN, KOD, NaOD and CBr4 and rhombohedral RbNO3
are reanalyzed with direct multipole analysis. In these examples the
importance of coupling seems to grow with the complexity of the crystal.
Original language | English |
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Pages (from-to) | 274 - 285 |
Number of pages | 12 |
Journal | Acta crystallographica Section A: Crystal Physics, Diffraction, Theoretical and General Crystallography |
Volume | 38 |
Issue number | 2 |
DOIs | |
Publication status | Published - 1982 |
MoE publication type | Not Eligible |