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Origin of dark-channel X-ray fluorescence from transition-metal ions in water.

Research paper by Robert R Seidel, Samira S Ghadimi, Kathrin M KM Lange, Sébastien S Bonhommeau, Mikhail A MA Soldatov, Ronny R Golnak, Alexander A Kothe, René R Könnecke, Alexander A Soldatov, Stephan S Thürmer, Bernd B Winter, Emad F EF Aziz

Indexed on: 20 Dec '11Published on: 20 Dec '11Published in: Journal of the American Chemical Society



Abstract

The nonradiative dark channels in the L-edge fluorescence spectra from transition-metal aqueous solution identify the ultrafast charge-transfer processes playing an important role in many biological and chemical systems. Yet, the exact origin of such spectral dips with respect to the X-ray transmission spectrum has remained unclear. In the present study we explore the nature of the underlying decay mechanism of 2p core-excited Co(2+) in water by probing the nonradiative Auger-type electron emission channel using photoelectron spectroscopy from a liquid microjet. Our measurements demonstrate unequivocally that metal-to-water charge transfer quenches fluorescence and will inevitably lead to a dip in the total-fluorescence-yield X-ray absorption spectrum. This is directly revealed from the resonant enhancement of valence signal intensity arising from the interference of two identical final states created by a direct and Auger-electron emission, respectively.