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From the Early Days of Quantum Mechanics to Modern Analytical Practice: The History and Future of X-ray Absorption Spectroscopy

Gerald Seidler, University of Washington
Monday, February 12, 2024 - 4:00pm
PAA A-102

X-rays have found both fundamental and applied interest since their accidental discovery by Roentgen in 1895.  One of the longest-lived mysteries in x-ray science was the correct physical description of the fine structure that appears in the x-ray absorption spectrum of all materials.  This was first observed in 1920, but despite considerable theoretical effort a foundational description of the x-ray absorption fine structure (XAFS) was lacking until the 1971 work of our late UW colleague Ed Stern (Sayers, Stern, and Lytle, PRL 1971).  In that work, Stern and colleagues provided a scattering treatment of photoelectron physics encompassing both a predictive and an interpretive framework for XAFS.  The subsequent development and growth of XAFS capability at synchrotron x-ray light sources and the decades-spanning efforts by UW’s Professor Emeritus John Rehr and other theorists have together made XAFS a fully mature method that is undergoing rapid diversification.  While the typical XAFS user in 2000 was an x-ray expert frequently working on fundamental aspects of the XAFS phenomenon itself, the typical XAFS user in 2020 is likely seeking scientific impact in the materials science or chemistry of sustainability, the fundamental and applied aspects of catalysis, the development of new biological molecules for artificial photosynthesis or therapeutic use, or the environmental science or government regulatory considerations of human-made contamination in nature. The late 20th century work of physicists at the UW was a major contributor to this transformation of a curiosity of the interaction of photons with matter into a theory-informed experimental method with global scientific impact and the potential for global social impact.  In this talk I’ll review the history of XAFS and present some of the work that my research group has done in the last ten years to further enable and realize the analytical future of this quantum spectroscopy.

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