Colin wrote: > Can anyone suggest other sources of error which would be mitigated by having > different paths through the crystal. I don't think radiation damage > (mentioned by several people) is one.
Suggestion : any source of error which does not obey the crystal symmetries will benefit from redundancy. For instance assume that a small satellite is present and by coincidence one of the reflection from the secondary lattice is approximately on top of the lattice to measure. The secondary lattice diffraction obeys Friedel's law therefore I(hkl) and I(-h-j-l) will be equally affected. However in the general orientation - and assuming that we're not dealing with a triclinic crystal - the Bijvoet pairs for the satellite will not match those of the main crystal. Measuring the Bijvoet reflections will allow to detect a discrepancy among equivalent reflections which can be treated accordingly. By contrast by using a longer exposure time but without measuring the pairs one may measure more accurately (Poisson statistics) an incorrect result (reflection polluted by the contribution of a satellite). Thierry Notice: This e-mail message, together with any attachments, contains information of Merck & Co., Inc. (One Merck Drive, Whitehouse Station, New Jersey, USA 08889), and/or its affiliates Direct contact information for affiliates is available at http://www.merck.com/contact/contacts.html) that may be confidential, proprietary copyrighted and/or legally privileged. It is intended solely for the use of the individual or entity named on this message. If you are not the intended recipient, and have received this message in error, please notify us immediately by reply e-mail and then delete it from your system.
