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Nanostrukturen und Grenzflächen Poster: Do., 13:00–15:30 D-P285
Structural research on weakly bonded clusters with synchrotron radiation
Uwe Hergenhahn 1 , Silko Barth 1 , Volker Ulrich 1 , Sanjeev Joshi 1
1 Max-Planck-Institut für Plasmaphysik, EURATOM Association, Boltzmannstr. 2,
85748 Garching
Results of structural research on a beam of free clusters are reported.
We have carried out scans of the partial ion yield from H2O clusters along the O
K-edge. Since recently the NEXAFS spectrum of liquid water along the O K-edge
was reported [1] and interpreted with far reaching conclusions on the local structure,
it should be of great interest to compare to clusters. Results for the fragments from
clusters show features of both hexagonal, four-fold coordinated and broken-bond, threefold
coordinated structures in the interpretation of [1].
In NeAr heteroclusters, we can demonstrate a process of electronic relaxation by
autoionization, which allows the identification of nearest neighbor relationships in noncovalently
bonded systems from the kinetic energy of the autoionization electron. This
process was predicted in theoretical work and termed ICD (Interatomic Coulombic
Decay) [2]. Transitions of this type should exist in all or most van der Waals and
hydrogen bridge bonded systems.
[1] P. Wernet et al., Science 304 (2004) 995.
[2] L.S. Cederbaum et al., Phys. Rev. Lett. 79 (1997) 4778; J. Zobeley et al., J.
Chem. Phys. 115 (2001) 5076.
Fig. 1: Electron spectra from
a coexpansion of Ne and Ar.
When the beam is cooled sufficiently
to allow formation of
heteroclusters, a signal from
autoionization of Ne 2s hole
states into Ne 2p −1 Ar 3p −1
can be detected (left, bottom
panel).