Phase observation in an organic crystal (benzil: C₁₄H₁₀O₂) using long-wavelength X-rays

The phase-related asymmetry effect near a multi-beam excitation point has been observed for a noncentrosymmetric organic crystal, benzil (C₁₄H₁₀O₂), by using 3.5 keV X-ray synchrotron radiation. A multi-beam theoretical calculation shows good agreement with the experimental data when mosaic spread of the crystal is taken into account. A practical method to extract the cosine of the phase triplet for noncentrosymmetric crystals is also discussed.