The theory of diffuse scattering of X-rays by a molecular crystal

Abstract

The theory of diffuse X-ray scattering by a molecular crystal is given, it being stressed that the modes of vibration causing scattering are in general mixed translational and librational. The theory is applied to an idealized model of hexamethylenetetramine, making use of the elastic constants and the Raman frequency to determine some of the molecular interaction constants. Dispersion curves are calculated from which frequency distributions are obtained. These compare well with experimental data. The thermal diffuse scattering is calculated and compared with experiment, and with the predictions of more approximate theories. The similarity between all of these suggests that very careful measurement of X-ray intensities will be necessary before conclusions can be drawn about intermolecular forces in crystals.