Enantiomorph determination using inverse reference-beam diffraction images.

It is shown that enantiomorph structures of a noncentrosymmetric crystal can be determined, in the absence of anomalous diffraction signals, by measuring two series of reference-beam oscillation diffraction patterns related by an inverse-beam geometry. The corresponding intensities of the Friedel pairs recorded on the two sets of images exhibit the characteristic three-beam interference effects that provide the unambiguous phase information. The experimental arrangement and the data-analysis procedure are demonstrated through an experimental example on tetragonal lysozyme.