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Figure 4
Fourier analysis plots for the projection of plane group pg along the a axis (see Fig. 1[link]) with atom positions at x′1 = 0.1 and x′2 = 0.6 that allow investigation of the reflections along the b axis. The processing was performed in analogy to the description in Fig. 2[link]. As the obtained amplitudes thereby are all zero for the odd numbers of h′, it can be concluded that the extinction conditions for plane group pg along the b axis are Mathematical equation, which is in full agreement with the corresponding reflection condition (Mathematical equation) given in Volume A of International Tables for Crystallography. Moreover, it can be concluded the phase values for reflections with non-zero amplitude are not restricted since their B terms are not zero. Hence, the phase angles for h = 1 and 3 are zero because A(h) and B(h) are positive. According to equation 4[link] and the lookup table in Appendix A[link], h = 2 [+A(2), +B(2)] yields 72.5° for the structure-factor phase, and for h = 4 [−A(4), +B(4)] a phase value of 143.1° (= −36.9° + 180°) is obtained.

Journal logoCRYSTALLOGRAPHIC
COMMUNICATIONS
ISSN: 2056-9890
Volume 82| Part 2| February 2026| Pages 235-243
https://doi.org/10.1107/S2056989026000745
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