On the minimum number of beams needed to distinguish enantiomorphs in X-ray and electron diffraction

The minimum strategy for distinguishing enantiomorphs by dynamical diffraction is determined. It is found that, in the absence of anomalous dispersion, it is possible to determine the absolute hand of an enantiomorphic crystal by three-beam dynamical X-ray or electron diffraction in a general orientation only if a fourth noncoplanar reciprocal-lattice point can be identified. Three-beam dynamical diffraction alone is unable to distinguish enantiomorphic forms. Identification is possible using four or more dynamical beams, in general, unless all relevant structure factors lie on a plane in reciprocal space passing through the origin. Supporting computations are given.