The electronic structures of crystalline and aqueous solutions of NaBr and NaBrO3 using in-situ Na K and Br L edge x-ray absorption spectroscopy

Abstract

The electronic structures of crystalline and aqueous solutions of NaBr and NaBrO3 were studied using in-situ Na K and Br L edge x-ray absorption spectra measured under ambient conditions. Analyses of Na K-edge x-ray absorption spectra show that NaBr and NaBrO3 strongly dissociate in aqueous solution and form Na+ hydration structures, [Na(H2O)n]+ (n = 0–6). However, the size of the anions significantly affects the formation of the Na+ hydration structures in aqueous solutions. The ligand field potential (10 Dq) observed in the Br L-edge x-ray absorption spectra allows in determining their dependence not only on the coordination structure between the Br and the first near neighbor but also the second near neighbor in crystalline state, and, the hydration structure and the counter cations in aqueous solutions. DV-Xα molecular-orbital calculations predict that the transitions in the Br L-edge NEXAFS occur from Br 2p to the unoccupied states containing mainly 4d orbitals of Br for both crystalline and aqueous solution. However, 5s and 5p of Br and 3p of Na in addition to the 4d orbitals of neighbor Br for crystalline NaBr and 5s and 5p of Br, 2p of O and 1s of H for aqueous NaBr also contribute to the unoccupied states.