PSI-SCANS

4.21 - PSI_SCAN absorption correction

Synopsis
This routine uses the method described by North, Phillips and Mathews , and is specific for CAD4 data. Up to 10 psi-scan sets may be processed and the present implementation has an important restriction in that ALL sets must contain the SAME number of measurements for the SAME incremental psi-angles. This is because this data is averaged in the calculation of the transmission surface.
The psi-scan curve may be Fourier smoothed and specified curves may be omitted from the averaged transmission surface. A theta (spherical crystal) correction may also be applied. Graphical output is provided to display the original psi-data, the averaged psi-curve and Fourier smoothed psi-curves, and a final comparison between the corrected and uncorrected data. Once the transmission surface has been adopted, a corrected reflection file may be written using the Process menu item. If direction cosines are present in the uncorrected file name.HKL, these will be echoed to the corrected output file.
NOTE The approximations inherent in the psi-scan method make it unsuitable for highly absorbing crystals. For these samples a GAUSSIAN or ANALTYICAL or refined absorption correction should be used.

Files read
  1. name.INS (for unit cell information only).
  2. name.HKL - uncorrected reflection file.
  3. name.PSI (or PSI.DAT) - CAD4 diffractometer file containing psi-scans.
Files written
  1. PSI_SCAN.HKL - absorption corrected reflection file
  2. PSI_SCAN.LST - List file giving summary of the applied corrections
  3. PSI_SCAN.CIF - CIF containing relevant information