XANES spectroscopic studies at L3 edge of 79Au in its various chemical forms

Abstract The systematic X-ray absorption near edge structure (XANES) investigation at Au L3-edge was made on Au in metallic form and its compounds in various definite oxidation states, viz., Au(OH)3, AuCl, AuCl3, HAuCl4, AuI and AuBr3. The spectra have been recorded with linearly polarized photon beam from 2 GeV INDUS-2 Synchrotron source. All XANES spectra were deconvoluted to configure the energy positions of bound and continuum state transitions. With respect to the reference metallic Au, the absorption edge of the Au-compounds shifts towards higher energies with increasing valency of the absorbing atom. The origin of different shifts is found to be dependent on the charge transfer mechanism between Au and ligands in the measured spectra at Au L3-edge. The shifts in the absorption energies have also correlated to an increase in the ligand field strength. The continuum state energy and areas of the pre-edge peaks for the Au-compounds with Au in +3 oxidation state increases systematically in the spectrochemical series as AuBr Au(OH)3, which indicates hybridization of d-orbitals and increasing tendency of ligand atom to attract electrons. Theoretical simulations are in line with this trend and the Au-series demonstrates that energy shifts in XANES spectra of Au(III) compounds can be understood in terms of crystal field theory.