title: Phase determination by wavelength-modulated diffraction. I. Centrosymmetric case.
abstract: Wavelength-modulated diffraction was developed by Iwasaki, Yurugi & Yoshimura [Acta Cryst. (1999), A55, 864-870] as a method for phase determination, in which the intensity of Bragg reflections is recorded using radiation whose wavelength is changing continually over a range in the vicinity of the absorption edge of an atom in the crystal. Using a ferrocene derivative crystal (chemical formula C36H32O7Fe, space group P2(1)/a) with the Fe atoms chosen as anomalous scatterers, measurements were made of the intensity gradient dI/d lambda of the reflections with an imaging plate as a detector on a synchrotron radiation source at Ritsumeikan University. In the case of a centrosymmetric crystal, the phase of the structure factor could be derived by measuring only the sign of dI/d lambda at one wavelength in the range. Of 104 reflections measured, the correct phase was assigned to 101 reflections. A discussion is given on the errors involved and on the limits of application of the method.
authors.affiliation: Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Koganezawa
authors.forename: Y
authors.initials: Y
authors.lastname: Yoshimura
authors.forename: N
authors.initials: N
authors.lastname: Nakamura
authors.forename: H
authors.initials: H
authors.lastname: Iwasaki