W0082

Photocrystallographic Data Collection from Transient Species at the SUNY X3A Beamline at NSLS. G. Wu, C. Kim, S. Pillet and P. Coppens,

Dept. of Chemistry, SUNY at Buffalo, Buffalo, NY 14260

The photocrystallographic data collection system at the NSLS SUNY X3A beamline [1,2], which includes a synchronized X-ray chopper and pulsed laser, has been extensively modified to allow collection of diffraction data from transient species with life-times down to 50(s. The scheme of data collection and analysis is described in Fig. 1. A modification of the SMART program allows a double-(laser-off/laser-on)-scan across the identical phi range in adjacent frames, thus enabling direct comparison of the diffraction patterns from the dark and illuminated crystal.

The laser-on/off intensity differences are analyzed by the program ‘On-Off Analyzer’. Finally, a new version of the program LASER [2] refines the excited state structure from the laser-on/off data sets.

A first stage data collection has been done using a (TEA)₄Pt₂(H₂P₂O₅)₄ crystal [3]. The results indicate that repeated measurements are required to achieve the desired accuracy.

[1] Fullagar, W.K.; Wu, G.; Kim, K.; Ribaud, L.; Sagerman, G.; Coppens, P. J. Synchrotron Rad. 2000, 7, 229.

[2] Ozawa, Y.; Pressprich, M.R.; Coppens, P. J. Appl. Cryst. 1998, 31, 128.

[3] Kim, C.; Wu, G.; Coppens, P. to be published.

Fig. 1. Scheme of Data Collection and Structure Refinement.

Acknowledgements: Work supported by the NSF (CHE9981864) and DOE (DE-FG02-86ER45231). The NSLS is supported by the US Department of Energy, Division of Materials Sciences and Division of Chemical Sciences.