The structure and Bijvoet ratios of cadmium selenide

The structure of cadmium selenide has been determined from X-ray intensity data obtained with extended-face crystals. The wurtzite parameter u was found to be 0.37679 ± 0.00012. Comparison of the intensities of equivalent reflexions provided a test for the internal consistency of the measurements. Equivalent reflexions in two specimens differed on average by 1.4 and 0.6% from the mean measured intensity, attesting to the high internal consistency of measurements from extended-face crystals. Comparison of 36 structure factors derived from data obtained from both specimens showed their average deviation from the mean to be 0.9%. An attempted least-squares refinement of the dispersion corrections of both atoms from observed Bijvoet ratios failed, presumably on account of correlation. When the dispersion corrections of one atom were held constant, it did prove possible to refine the dispersion corrections of the other atom.