Wavelength-Modulated Diffraction. A New Method for the Phase Determination of the Structure Factor

Abstract

A new diffraction method has been proposed in which Bragg reflections are recorded with changing continually the wavelength of synchrotron radiation in the vicinity of the absorption edge of an atom contained in a crystal. It is shown that the intensity gradient with the wavelength of the h k l reflection is in a simple relation to the real and imaginary parts of the structure factor of that re-flection and, if the positions of the anomalously scattering atoms are known or properly assumed, the phase of F(h k l) can be derived by solving two simultaneous linear equations. The procedure is particularly simple when the crystal is centrosymmetric. The method, called the wavelength-modulated diffraction method, is free from the problem of intensity scaling encountered in other methods of phase determination.