Hello Jakub, it sounds  strange, How much were shifted the 2nd and 3rd reflection? I suppose you have excluded any experimental error, but you can try an internal standard, just check my paper in CCM 47 (1999) 113. BR, M.

Dear Jacub,

very strange as Marián said above.

Can you share your diffractograms?; so we can easily see how much the high order peaks shift and how the relative peak heights change. So we might get 'new' ideas.

Thanks in advance.

can you share what the molecule is?  Is it possible that the new orientation of the organic molecule is still such that the d-spacing would not change?

Thank you for your comments. I have attached the XRD patterns of 3 samples: green (starting material), red (after UV light), blue (after Vis light). The intercalated molecule is azobenzene together with primary dodecylamine.

The shift is not significant, only about 0.7 A. However this is repetitive and reversible. It seems that azobenzene isomerization affects 2nd and 3rd order, but the interlayer distance of the mineral is constant.

I was just wondering how to explain such phenomenon (constant 1st, changes of 2nd and 3rd order) in general? Is it connected with some local ordering of molecules in the interlayer which causes diffraction just at certain angles?

Hello Jakub,

You know this Ph.D. thesis?

https://books.google.com.br/books?id=ZBjuRXkZkgIC&pg=PA3&lpg=PA3&dq=azobenzene+decompose+under+uv-light&source=bl&ots=T6Lq5Gdxtk&sig=Yo8zboboNIwpvbjrjhkS4Q3W9BI&hl=pt-BR&sa=X&ved=0ahUKEwjE1vzp9u7RAhVDiZAKHZ67CT0Q6AEIHjAB

You consider the possible photodecomposition or also the photodimerization of the molecules. This changes not properly will promotes changes on the basal space (1st order reflection).

Thank you, Jakub, for sharing your data.

But sorry Jakub,

but I cannot really see a peak shift of your 3rd-order peak (popping up around  35°). This may be due to your strongly nonlinear angular scale.

The 1st-order and the 2nd-order peaks  also remain almost at the same positions, but the profiles change a little bit.

I would not draw any (high sophisticated) conclusion with respect to UV/Vis optical modifications/damage/decomposition of your molecules or other significant change of your sample.

These tiny differences may be due to experimental issues such as inhomogeneity or irreproducibility of positioning the sample etc.

Please do not believe in the results of an evaluation software unless you can really  see them directly by your own eyes.  

Thank you all for comments. I will get back to you when I will have more data on this complex.