Niobium LIII and LII X-ray absorption-edge spectra of Nb2O5 and NH4NbF6

The LIII and LIIabsorption-edge spectra of Nb(V) in Nb2O5 and NH4NbF6 are carefully measured and the subtle differences are found between the Nb2O5 and NH4NbF6 spectra. These spectra are interpreted in terms of molecular orbital (MO) theory. The absorption-edge spectra consist of a strong double-peaked edge structure related to the empty MO s 2t2g (π∗) and 3e(σ∗) and a weak peak associated with the empty MO3a1g(σ∗) in the octahedral clusters NbL6 (L  O, F). Significant differences are also found beween the Nb LIII and Nb LII absorption-edge spectra.