title: X-ray Birefringence: A New Strategy for Determining Molecular Orientation in Materials.
abstract: While the phenomenon of birefringence is well-established in the case of visible radiation and is exploited in many fields (e.g., through the use of the polarizing optical microscope), the analogous phenomenon for X-rays has been a virtually neglected topic. Here, we demonstrate the scope and potential for exploiting X-ray birefringence to determine the orientational properties of specific types of bonds in solids. Specifically, orientational characteristics of C-Br bonds in the bromocyclohexane/thiourea inclusion compound are elucidated from X-ray birefringence measurements at energies close to the bromine K-edge, revealing inter alia the changes in the orientational distribution of the C-Br bonds associated with a low-temperature order-disorder phase transition. From fitting a theoretical model to the experimental data, reliable quantitative information on the orientational properties of the C-Br bonds is determined. The experimental strategy reported here represents the basis of a new approach for gaining insights into the orientational properties of molecules in anisotropic materials.
authors: †School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales.
authors: Benjamin A
authors: BA
authors: Palmer
authors: †School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales.
authors: Gregory R
authors: GR
authors: Edwards-Gau
authors: †School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales.
authors: Anabel
authors: A
authors: Morte-Ródenas
authors: †School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales.
authors: Benson M
authors: BM
authors: Kariuki
authors: †School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales.
authors: Gin Keat
authors: GK
authors: Lim
authors: †School of Chemistry, Cardiff University, Park Place, Cardiff CF10 3AT, Wales.
authors: Kenneth D M
authors: KD
authors: Harris
authors: ‡Harwell Science and Innovation Campus, Diamond Light Source, Didcot, Oxfordshire OX11 0DE, England.
authors: Igor P
authors: IP
authors: Dolbnya
authors: ‡Harwell Science and Innovation Campus, Diamond Light Source, Didcot, Oxfordshire OX11 0DE, England.
authors: Stephen P
authors: SP
authors: Collins
keywords: X-ray birefringence; molecular orientation; phase transition; solid inclusion compound; synchrotron