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X-ray Absorption Spectroscopy

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.
Stockholm University |AlbaNova University Center| Fysikum |Updated 14 June 2010 | back to top |