Analysis of orientationally disordered structures. IV. Correlations between orientation and position of a molecule

The concept of a 'rotational form factor' analysis of molecular crystalline structures is generalized by allowing correlations between the orientation of a molecule and its centre-of-mass position. This coupling results in correction terms to the well known rotational form factor. The method is illustrated with the example of (i) tetrahedral molecules and (ii) dumbells at a site of cubic symmetry (m3m) and the rô1e of the site symmetry as well as the magnitude of the mean-squared amplitude (u²) of the centre-of-mass motion are investigated.