I second Phil's opinion - it is better to scan and be sure - as long as the scan results are not hideously abnormal. If you cannot scan for whatever reason but are sure that the X-ray optical system is properly calibrated - then use Phil's numbers below :)
Artem > Always take the scan results ahead of the typical values unless they are > obviously wrong. Only use the "predicted" values if the scan is broken > or too weak (e.g. very small crystals) and in that case I'd be tempted > to add 10-20 eV to the "typical" peak wavelength to make sure you > weren't actually collecting the inflection point since they are > typically very close in SeMet. > > In my NSLS X29-dominated data collections, I find I end up using > something like this for non-oxidized SeMet: > > Peak: 12664 eV, 0.9790 Angstrom (usually in range 12662-12664) > Infl: 12662 eV, 0.9792 Angstrom (usually in range 12660-12662) > I also typically use high energy remote: 12860 eV, 0.964 Angstrom > > give or take a few eV. This tends to translate well between the > relatively small number of beamlines that I personally end up using. > But I always prefer to take the results from the Chooch analysis of the > scan from the actual crystal. > > Cheers (and good luck) > Phil Jeffrey > Princeton > > > Jerry McCully wrote: >> Dear All: >> >> Next week we are going to try some seleno-Met labeled crystals. >> >> We checked the literature to try to find out the peak wavelength >> that has been used for SAD or MAD data collection. But they are slightly >> different ( may be 50 ev) in different papers. >> >> I guess this is due to the discrepancy between the fluorescence >> scanning and the theoretical vaules of f' and f''. >> >> When we collect the data, which wavelength should we use? Should >> we trust the scanning results? >
