Dear Laurie, I think you may be dealing with a modulated structure, superposition of multiple lattices or a lattice-translocation defect, it is hard to judge based only on the diffraction pattern profile. For the first case, I would suggest to have a look at Porta et al. 2009 (Acta Cryst. D67, 628-638), where they describe the usage of Eval15 to process the data. In this scenario, the position of the satellite reflections can be described by an extra vector q, which can have from 1 to 3 components and it is added to the canonical scattering vector S (see also Wagner et al., 2009, Acta Cryst. B65, 249-268). However, from your image, the spots are not resolved inside the streaks, indicating that perhaps this is not the case. For the second case, I would recommend Sauter et al., 2010 (Acta Cryst. D43, 611-616), where the usage of LABELIT is described to deal with superposed lattices. For the third possible case, the lattice-traslocation defects, it is important to define how a translocation can occur between the two lattices (see details in Wang et al., 2005, Acta Cryst. D61, 67-74). Their diffraction images look very similar to yours. You do not comment whether you were able to perform data reduction. I suspect that it would be rather difficult, although the integration programs may reject the streaks at a certain price in terms of integration statistics etc. In any case I would recommend to deal with the issue as early as possible, i.e. data collection stage or indexing stage, to avoid of carrying the problem over into the next steps of structure solution / structure refinement. Out of curiosity, it would be nice to know the appearance of the streaks, if you collect data with fine slicing (i.e by using a Pilatus detector) or with a kappa goniometer (you may have already done this of course). Do you see these streaks in all crystal orientations? Can you resolve spots within the streaks and what is your resolution?
Good luck! Best wishes Dr. Ivan Campeotto Imperial College London London, UK
