E0214

A New Coupled-Axis Scan Technique For Indexing and Accurate Latice Determination On The Nonius KappaCCD. Rob Hooft of Nonius B.V. Rontgenweg 1, Delft, The Netherlands

The traditional method to determine the unit cell from small molecule area detector data uses diffraction spots from a number of rotation images. For these spots, the locations on the detector can be accurately determined. The estimate for the crystal rotation angle (phi) at which the diffraction takes place is, however, in comparison very approximate. The angles of the unit cell determined from such basically 2-dimensional data are intrinsically unreliable. As these unit cell angles are very important in the determination of the Laue group, and hence in the decision process for the data collection strategy, the inaccuracy is to be avoided if possible.

Using a goniostat with Kappa geometry and a specially designed combination of scans we are able to calculate very accurate cell parameters without using time-consuming data acquisition techniques.