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I threw this image of one of my protein crystal's diffraction pattern (not the greatest) on a poster, and was wondering where (what reciprocal dimension) the ice rings are located as it might be a useful reference (or talking point).

While I can find information about water ice's unit cell parameters (4.5 Å, 7.3 Å), I'm not sure if these are where the reflections would be located (the inner two rings seem far too close for that disparity, and I believe the outer two rings are at a much higher resolution (< 3 Å)

enter image description here

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Is this off-topic or otherwise bad for Physics.SE? –  Nick T Nov 12 '11 at 3:05
    
No, I think this is a great question. The downvote is odd, because if there is a good reason for it, it is certainly not an obvious reason. –  Colin K Nov 12 '11 at 3:48
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I assume that somebody didn't like a question with no mention of string theory or symmetry groups. :) –  Colin K Nov 12 '11 at 3:50
    
I didn't DV, but I can see why - the "ice rings" are more properly called "DeBye-Scherrer" rings, and their precise location will depend on the wavelength of the incident radiation. Further, the diffractograms are typically pictures of reciprocal space, so discussing the d-spacing of ice on a reciprocal space map requires some basic calculation, but it is not evident from the picture which map is used. So, question at its heart is a good one, but as written is riddled with errors. –  Jen Nov 12 '11 at 10:37
    
Jen described the reasons for my downvote very well. No geometry of this "poster", no wavelenth, just hope others will do the thinking for him. –  Georg Nov 12 '11 at 11:16
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1 Answer

I finally found a source; according to Peter Nollert, ice rings are located at:

  • 3.897 Å,
  • 3.669 Å,
  • 3.441 Å,
  • 2.671 Å, and
  • 2.249 Å.

My frame seems to be missing one of the three 3 Å rings, but the 2 Å rings seem plausible.

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