OK, I did play about & display some Q-space (Q=2pi/d) plots in GSAS. It will be an option in the next release. Pretty similar to conventional 2-theta plots - just a slight "squishing" of the scale at the upper end. Might not be really desirable for complex patterns. Some TOF data where data was collected to quite small TOF will need to have different limits picked by the user to see anything (plot dominated by large Q range). However, please don't be tempted to collect constant Q-step data; the programs/peak shape functions really do expect 2-theta/TOF scans. Alan Coelho's remark does raise an issue about such data & how it was really collected. Q-Step scans would probably just be an "oddly stepped" conventional step scan but slew scans split into constant Q steps would be a different matter. Beware of the Law of Unintended Consequences. Bob
R.B. Von Dreele IPNS Division Argonne National Laboratory Argonne, IL 60439-4814 -----Original Message----- From: Alan Hewat [mailto:[EMAIL PROTECTED] Sent: Wednesday, February 21, 2007 9:45 AM To: rietveld_l@ill.fr Subject: RE: Powder Diffraction In Q-Space >Depends on the lattice? Cubic patterns look great in old "Q": >eg: "Tables of Q as a Function of 2theta" Acta Cryst 12, 421, (1959) >... where Q was 10^4/d^2. Yes, it does "en principe" depend on the lattice of course :-) but 10^4/d^2 still provides a better "constant peak density scale" than any other simple function I can think of. Certainly a lot better than a linear d-spacing scale. And yes, this is not a new idea. Alan. _____________________________________________________________ Dr Alan Hewat, ILL Grenoble, FRANCE<[EMAIL PROTECTED]>fax+33.476.20.76.48 +33.476.20.72.13 (.26 Mme Guillermet) +http://www.ill.fr/dif/people/hewat/ _____________________________________________________________
