Anisotropy in the variation of serially-measured integrated intensities.

Many crystals suffer radiation damage on exposure to X-rays. The resulting variation (often decline) in intensity standards measured during a typical X-ray diffraction structure determination is typically corrected by an isotropic polynomial expression. A linear decline is reported in many studies. In the anisotropic case, the additional variation may be represented by the coefficients of an ellipsoid. The results of applying the new anisotropy relation both to an organometallic and an inorganic structure are presented. The anisotropy found may be pronounced for severe radiation damage. For the two cases investigated, the linear anisotropic correction leads to significant reduction in R(int,) with only minor improvement resulting from the inclusion of exponential terms. Simple isotropic correction, based on a small number of standards, may introduce significant error.