XAFS-related entries in the online dictionary of crystallography

More than 12 000 papers concerning X-ray absorption techniques have been published over the last five years and the XAFS Commission's (CXAFS) contribution to the IUCr Dictionary has been considered a priority. One important objective of this endeavor was to identify ambiguous or incorrect usage of XAFS expressions in the scientific language. Our objective was not to formulate "perfect" definitions, but to propose currently used definitions that could eventually be improved through an open debate.

In 2009, the CXAFS created a Working Group on XAFS Nomenclature (WG) and, to ensure a clear connection between CXAFS and IXAS (International X-ray Absorption Society), both communities were represented in the membership of the WG.

P. Glatzel (CXAFS and IXAS-DE) has been nominated to coordinate the WG. Other members are: C. T. Chantler (CXAFS-AU), A. M. Molenbroek (CXAFS-DK), M. Newville (IXAS-US), J. Rehr (Theory-US), Tsun-Kong Sham (IXAS and Theory-CA) and R. Strange (Biology-UK).

Proposed definitions have been reviewed by seven members of the Advisory Committee (AC). They are C. Brouder (FR), D. Creagh (AU), J. Garcia (ES), C. Natoli (IT), J. Penner-Hahn (US), R. Sarangi (US) and E. I. Solomon (US).

The WG and the AC are formed by experimentalists and/or theoreticians having a physical or chemical or chemical-physical background. These different backgrounds result in the description of the same phenomenon with different approaches and different terminology. For example, the item "absorption threshold", which is currently used by all XAFS experts, has been considered tricky to define by nearly all WG and AC members. Consequently, several definitions, reflecting theoretical or experimental approaches, have been proposed.

AC members have sent detailed reports, indicating comments, corrections and, in some cases, proposing alternative definitions to the XAFS Commission Chair, who transmitted anonymous reports to P. Glatzel.

In the revised document, the WG has taken into account nearly all suggestions and is indebted to F. Neese, F. de Groot, A. Kotani and S. Huotari for their advice and valuable contributions concerning some definitions.

The revised document has been approved by each AC member, with minor corrections included in the final document.

I am grateful to all colleagues for their precious contributions, in particular C. T. Chantler for his continuous and efficient support, P. Glatzel, for the coordination of the WG and Y. Joly for stimulating discussions.

XAFS related definitions are included on the IUCr XAFS Commission website. The revised text is a compromise in order to obtain definitions with a consensus as large as possible. In order to open the debate, minority or specific comments, from WG and AC members or other experts, will be in a separate document on the XAFS Commission web site. This and the next XAFS Commission will monitor comments for two years. After this period, entries will be eventually revised.

Finally, I would like to take this opportunity to warmly thank Sine Larsen, IUCr President, and all Executive Committee Members, as without their continuous and encouraging support this work could never be possible.

Isabella Ascone, Chair of the CXAFS

Dictionary entries