Determination of the position of even the lighter anomalous scatterers in a crystal structure by means of a two-wavelength technique

For identical anomalous scatterers among a majority of normal scatterers the structure-factor amplitudes are estimated from intensity data obtained either with two wavelengths at one side of the absorption edge or with one wavelength at either side. Direct methods (or a Patterson synthesis) will allow the localization of these anomalous scatterers. Test calculations on the known structure of the iron-containing protein ferredoxin, simulating the effects of synchrotron radiation, show the feasibility of the procedure.