# Four Circle Diffractometer Measurements in Single Counter Mode

# Reflection List Processor

This section describes the means for doing a standard single counter four circle diffractometer measurement with SICS. A prerequisite for that is a file with a list of reflections to measure. This is a simple file with three floating point values per line giving the HKL of the reflection to measure. Do not forget to put standard reflections into that file any now and then. Another prerequisite is, that the UB-matrix had been determined beforehand and that SICS has the updated values. Also check the value of lambda in the hkl-object.

The measurement procedure is rather simple: If a reflection is accessible the diffractometer is positioned on that reflection. Then a scan is done for the reflection and data written to file. The scans all run with a fixed scan widths, counter preset and countmode. There is a choice of omega scan or omega two theta scan. It is known that there are more sophisticated measurement schemes for four circle diffraction, but as TRICS is only temporarily operated with a single counter not much optimisation seemed necessary.

Three files will be written starting from a root such as tricsnumberyear. For instance trics05601998 means file number 560 in 1998. The file ending in .log will contain the console log. This is extremely verbose. Another file ending with .col will contain the reflection, diffractometer settings and the measured profile. The third file, ending with .rfl will contain for each refelction, the HKL, the diffractometer settings and the intensity and sigma intensity as calculated by the SICS internal integration routine. It does a Grant Gabe integration (see J.Appl. Cryst (1978), 11, 114-120).

For the purpose of the command description it is assumed, that this facility is accessible as object mess within SICS. Interaction with this object happens through the following commands:

mess start
  Creates a new set of files and writes some header info.
mess measure filename iSkip
  Starts a measurement. Reads reflections from the file filename. iSkip is an optional parameter which allows to skip iSkip lines in the file. This is for recovery in cases of accidental or purposeful interruption of the measurement.
mess genlist filename iSkip
  Mesures reflection from filename. The file is expected to have been created by hklgen and to include all the angle settings. The optional parameter iSkip determines the number of lines to skip in the file. This feature allows to continue measurement on not fully processed files.
mess reopen filename
  Reopens an already existing file set for appending. Only the file root without directory info or endings needs to be given.
mess close
  Closes the current data file set.
mess file
  Prints the current data file name.

Then there are a few parameter commands. They follow the general scheme:

mess parameter
  Prints the current value of the parameter
mess parameter value
  Sets the parameter to the new value.

This object knows about the following parameters:

countmode
  The counting mode to use. Possible values are timer or monitor.
preset
  The preset to use for counting
mode
  The measurement mode. Posssible values are omega for omega scans and omega2theta for omega two theta scans.
np
  number of points to collect for each profile.
step
  The step width in omega to use for scanning.
compact
  Determines if the scan data output to the SICS is in normal (compact = 0) or condensed (compact = 1) form. The default is 1.

mess supports two geometries: the first is the usual bisecting geometry. The second is the normal beam geometry where the detector is moved out of plane. This si accounted for by two switches:

mess bi
  switches into bissectiong mode. This is the default.
mess nb
  switches into normal beam mode.

This object supports some file management functionality. It caters for the problem that experiments may need to be continued. Thus reopening files and continuation of reflection processing at a point way down the reflection file is supported. Consequently the start of a new experiment requires the following steps:

- Create a new set of files with mess start.
- Configure the scans with the parameter commands.
- Start processing a reflection file with either the mess genlist or mess measure commands.

If you need to continue reflection file processing after an abort or after solving a problem the following steps are required:

- Determine the file number you were working at and the line number in the reflection file where you wish to continue processing.
- Set the file root with the mess reopen command.
- Configure the scan parameters again.
- Restart the measurement with either mess genlist or mess measure but specify the iSkip parameter according to the position in the reflection file where processing should continue.