Origin of Dark-Channel X-ray Fluorescence from Transition-Metal Ions in Water
journal contributionposted on 25.01.2012, 00:00 by Robert Seidel, Samira Ghadimi, Kathrin M. Lange, Sébastien Bonhommeau, Mikhail A. Soldatov, Ronny Golnak, Alexander Kothe, René Könnecke, Alexander Soldatov, Stephan Thürmer, Bernd Winter, Emad F. Aziz
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 Co2+ 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.