ELIMINATION OF EXTINCTION EFFECTS BY EXTRAPOLATION TO ZERO WAVELENGTH

A model-free approach to extinction correction of single-crystal refle ction data has been developed. Single-crystal peak-intensity observati ons taken over a series of wavelengths in the range 0.25-0.11 Angstrom were extrapolated to zero wavelength. Evaluation of this method by co mparison of extrapolated values with accurate kinematic structure fact ors for Si shows that it is capable of giving approximate independent estimates of extinction effects. The accurate synchrotron data of Hest er, Maslen, Spadaccini, Ishizawa & Satow [Acta Cryst. (1993), B49, 842 -846], which those authors believed to be unaffected by extinction, ha s been checked using the present method and found to be significantly affected by extinction. The present results give no reason to doubt th e validity of widely used extinction models.