TRANSFERABILITY OF DEFORMATION DENSITIES AMONG RELATED MOLECULES - ATOMIC MULTIPOLE PARAMETERS FROM PERYLENE FOR IMPROVED ESTIMATION OF MOLECULAR VIBRATIONS IN NAPHTHALENE AND ANTHRACENE

Earlier crystallographic refinements of naphthalene and anthracene against X-ray data recorded at five and six temperatures, respectively, have been repeated with atomic charge-deformation parameters transferred from a low-temperature study of perylene. Inclusion of these parameters causes the inplane molecular translation amplitudes to decrease, and those normal to the plane to increase, with respect to values obtained with the spherical-atom model. The revised translation tensors are systematically smaller than those predicted by published lattice-dynamical calculations but the librations agree somewhat better. Their temperature dependence shows no anomalous behaviour and accords qualitatively with the simplified model of Cruickshank [Acta Cryst. (1956), 9, 1005-1009].