REFLECTIONS WITH PHASE-ANGLE 0 OR PI IN NONCENTROSYMMETRIC SPACE-GROUPS

The imaginary parts of structure factors in centrosymmetric space grou ps disappear so that the phase angle of every reflection is either 0 o r ir. On the other hand, the phase angles of reflections in noncentros ymmetric space groups can have any value between 0 and 2 pi. However, some reflections in the noncentrosymmetric space groups under certain conditions behave just like those in the centrosymmetric space groups, which might help to solve the so-called crystallographic phase proble m. Reflections with phase angle of either 0 or pi in 157 noncentrosymm etric space groups extracted from International Tables for X-ray Cryst allography (1979), Vol. I (Birmingham: Kynoch Press) are tabulated.