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X-ray Absorption Spectroscopy
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| | In X-ray absorption spectroscopy (XAS) the
absorption coefficient of x-rays is measured in dependence of
the photon energy. By means of synchrotron radiation the energy
is varied in an energy range close to an absorption edge, where
core electrons are excited into unoccupied atomic/molecular
orbitals. These transitions lead to a pronounced fine structure,
so called XAS resonances. A XAS spectrum displays the density of
unoccupied states and therefore contains important electronic
information. Due the localization of the core hole which is
created at a certain atom the unoccupied states are projected on
this atom. the soft X-ray regime (K-edges of C, N, O) XAS
transitions are governed by Dipole selection rules and
consequently the absorption cross sections shows a polarization
dependent angular anisotropy. By means of dependent XAS
measurements it is therefore possible to determine orientation
of molecular adsorbates.
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