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Methoden und Instrumentierung Poster: Mi., 14:00–16:30 M-P90
The structure of liquids studied by resonant x-ray emission and absorption
spectroscopy in the soft x-ray range
Markus Weigand 1 , Oliver Fuchs 1 , Florian Maier 1 , Eberhard Umbach 1 ,
Michael Zharnikov 2 , Michael Grunze 2 , Lothar Weinhardt 3 , Marcus Bär 3 ,
Clemens Heske 3 , Jonathan Denlinger 4
1 Exp. Physik II, Universität Würzburg, D-97074 Würzburg – 2 Angew. Physikal.
Chemie, Universität Heidelberg, D-69120 Heidelberg – 3 Dept. of Chemistry, University
of Nevada, Las Vegas, NV 89154-4003, USA – 4 Advanced Light Source, Lawrence
Berkeley National Lab, Berkeley, CA 94720, USA
We have used resonant x-ray emission spectroscopy and x-ray absorption spectroscopy
in the soft x-ray range to study liquids. Employing these techniques to liquids is a
technically challenging task requiring a third-generation synchrotron source combined
with a high-efficiency grating spectrometer, and, last but not least, a liquid cell with
an ultra-thin window separating the liquid from the vacuum. Recently several groups
have started experiments with custom-made static cells. To overcome the problems
of these designs with beam-induced effects like gas bubbles and the precipitation of
material on the window, we have developed a flow-through liquid cell. In our design
the liquid in the probing volume is exchanged several times per second thus avoiding
such effects. Furthermore, it allows a fast switching of the investigated liquid, a change
of the concentration of a solved component, and the variation of the temperature within
the probed volume.
With this cell we have investigated the structure of various liquids including H2O,
D2O, NaOH, NaOD, acetic acid, and various aqueous solutions under well-defined
conditions. Our high-resolution spectra reveal details on the hydrogen bonding network
of water and its temperature-dependence. These spectra allow a direct determination
of the number of intact hydrogen bonds per molecule as a function of temperature.
Moreover, the different dynamics of H2O and D2O lead to pronounced isotope effects,
which are also present in the spectra of OH − and OD − ions. The technical design of
a new XES spectrometer and of the flow-through liquid cell as well as new results on
various liquids will be presented.
(financed by BMBF under contract no. 05KS4WWA/6 und 05KS4VHA/4)