RSCU-SOS - A RAPID SEARCHING AND CENTERING UTILITY ROUTINE FOR SINGLE-CRYSTAL X-RAY-DIFFRACTION STUDIES AT SIMULTANEOUS HIGH-PRESSURES AND TEMPERATURES

Single-crystal diffraction studies conducted in a diamond-anvil cell ( DAC) under high pressure (P) acid temperature (T) conditions often hav e the annoying problem that the sample orientation changes when P and/ or T is changed. It is essential to quickly find and recenter the diff raction peaks in order to refine a new orientation matrix and further collect diffraction data from the single crystal at the changed P-T co nditions. This paper presents a rapid searching and centering utility (RSCU) routine to deal with the orientation-shifting problem in high-P -T DAC single-crystal diffraction studies. The RSCU routine starts wit h a refined reflection list from previous PT conditions and conducts a search in the pattern of a spiral of open square (SOS) for diffractio n peaks in the chi-phi plane. Following the peak search, it conducts 2 theta, omega and chi scans to center the diffraction peaks and then p erforms a least-squares curve fit to refine the true diffraction posit ions in 2 theta, omega, chi and phi space. The RSCU routine incorporat es the Hamilton method to eliminate errors due to sample misalignment. Reflections are sorted to minimize the driving time between successiv e peaks. The algorithm of the routine is given in symbolic logic so th at it can be translated and inserted into other crystallographic softw are packages.