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Figure 3
(a) Schematic diagram of chitin fibre rotated by varying tilt angle α. (b) Two equivalent ways of rotating a fibre to a specific 3D orientation: the (α, β) convention used for the model evaluation and the (γ, α′) option [equations (7) and (8)]. (c-i) to (c-iii) For (002) (red), (110) (blue) and (013) (green), I(χ) is plotted for increasing χ over 0–360°. (d-i) to (d-iii) Enlarged insets for each case around the main peaks below 180° azimuthal angle. A different α range is plotted in each case to show the changes more clearly. Vertical dotted lines from the top x axes indicate the azimuthal peak position [for (013), the left-hand split peak is taken as the peak position]. Vertical dot-dashed lines from the bottom x axes indicate the left-hand side of the angles at half-width at half-maximum (HWHM). Horizontal dashed lines indicate the half-maximum intensity. Horizontal block arrows are guides to the eye, indicating shifts of the peak centres, FWHM [full width at half-maximum, for the (002) and (110) reflections] or HWHM [for the (013) reflection]. (e-i) to (e-iii) Model predictions of changes in the FWHMs for the (002) and (110) reflections and in HWHM for the (013) reflection with varying tilt angle α. (f-i) Intensity ratio of the azimuthal peaks at 90° to 270° [I(90°)/I(270°)] for the (002) reflection with varying tilt angle α. (f-ii) and (f-iii) Azimuthal peak positions of the (110) reflection (at ∼180°) and the (013) reflection as indicated by the dotted vertical lines in panel (d-iii), plotted with varying tilt angle α. The relevant relations are given in equations (S8), (S11), (S13), (S15), (S18) and (S28) in the supporting information.

IUCrJ
Volume 13| Part 1| January 2026| Pages 63-76
ISSN: 2052-2525
https://doi.org/10.1107/S2052252525009686