Some Comments on Rint - PowerPoint PPT Presentation

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Some Comments on Rint

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  1. Some Comments on Rint • For a good crystal Rint is < 10% • For even a bad crystal Rint<20% • For a good crystal the % of data removed is <1.5% • For a bad crystal <8%

  2. Very Large Values • Sometime get very large values for both Rint and % removed. • This always means you are in the wrong crystal class • Example monoclinic with beta = 90 • Tetragonal that is orthorhombic

  3. Data Reduction • The data measured is inensity • It needs to be converted to Fobs or Fobs2 • There are two corrections. • Polarization –because x-ray beam is not polarized and diffraction is not in plane of polarization =(1+cos22q)/2 • Lorenz Factor is a function of the instrument type and setup • |F|=(I/Lp)1/2

  4. Look at EVAL

  5. What have we done so far? • Found and mounted a crystal • Checked its quality • Determined the unit cell • Collect a set of frame data • Integrated the frames • Scaled the frames—combined equivalent reflections • Reduced the data • Formatted the data

  6. What is next for the data • Correct for absorption if needed • Integrated absorption correction • Empirical absorption correction • A “fudge” correction later • If we are going to do a correction a file containing direction cosines on unaveraged data is required • Correct for decay if needed