Chemical shift of Mn and Cr K-edges in X-ray absorption spectroscopy with synchrotron radiation

摘要

Mn and Cr K X-ray absorption edges were measured in various compounds containing Mn in Mn~(2+), Mn~(3+) and Mn~(4+) oxidation states and Cr in Cr~(3+) and Cr~(6+) oxidation states. Few compounds possess tetrahedral coordination in the 1st shell surrounding the cation while others possess octahedral coordination. Measurements have been carried out at the energy dispersive EXAFS beamline at INDUS-2 Synchrotron Radiation Source at Raja Ramanna Centre for Advanced Technology, Indore. Energy shifts of ~8-16 eV were observed for Mn K edge in the Mn-compounds while a shift of 13-20 eV was observed for Cr K edge in Cr-compounds compared to values in elemental Mn and Cr, respectively. The different chemical shifts observed for compounds having the same oxidation state of the cation but different anions or ligands show the effect of different chemical environments surrounding the cations in determining their X-ray absorption edges in the above compounds. The above chemical effect has been quantitatively described by determining the effective charges on Mn and Cr cations in the above compounds.