  We investigated the recently found superconductor LaO_{1-x}F_xFeAs by X-ray
absorption spectroscopy (XAS). From a comparison of the O K-edge with LDA
calculations we find good agreement and are able to explain the structure and
changes of the spectra with electron doping. An important result from this edge
is a limitation of the Hubbard U to values not significantly larger than 1 eV.
  From experimental Fe L_2,3-edge spectra and charge transfer multiplet
calculations we gain further information on important physical values such as
hopping parameters, the charge transfer energy Delta, and the on-site Hubbard
U. Furthermore we find the system to be very covalent with a large amount of
ligand holes. A shift in the chemical potential is visible in the O K- and Fe
L_2,3-edge spectra which emphasizes the importance of band effects in these
compounds.
