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Figure 1
Illustration of the projection procedure described in the main text. For plane group symmetry pg (International Tables, No. 4) the two shown atom positions are related by a glide line g (- - -) normal to the a axis. To allow the analysis of the extinction rules along the two principal axes in one dimension, the atoms must be projected onto lines as shown. This yields a point symmetric atom distribution on the line for the projection along the b axis and a non-symmetrical atom distribution for the projection along the a axis. In the one-dimensional models, the cosine and sine Fourier waves of order h′ will pass the one-dimensional unit cell in the direction of the arrows. A representation that shows a set of 3rd order cosine waves that traverse the unit cell is given in Fig. 2[link]. Thus, the projection along the b axis is used to study the extinctions along the a axis and vice versa.

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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