Scan-truncation corrections in single-crystal diffractometry: an empirical method

A satisfactory model for experimental θ-2θ scan profiles of single-crystal diffraction intensities can be obtained by convoluting the spectral dispersion with the intrinsic profile and then with a third angle-dependent function which we call an 'aberration function'. The first of these functions is calculated on the basis of theoretical components, while the other two are obtained from experimental measurements. The process includes accurate measurement of the inherent background, smoothing the profiles by Fourier analysis and synthesis, deconvolution and least-squares treatments. The method has been applied to data collected at 23 K, up to 2θ_Mo = 100°, from a spherical crystal of L-alanine. Model profiles are in excellent agreement with the experimental ones, and were used to evaluate truncation losses for several scan ranges. For the instrumental configuration of the diffractometer used in this investigation, scan-truncation losses are far larger than predicted by previous studies.