Observation of Raman components in resonant X-ray emission spectra of Fe cyanide

Abstract

There were two theoretical calculations to reproduce the Fe 2p absorption spectrum of hexacyanoferrate [R. K. Hocking et al., J. Am. Chem. Soc. 128 (2006) 10442, and Y. Nanba and K. Okada: J. Phys. Soc. Jpn. 79 (2010) 114722], but there was a big difference in the parameters used in both. To confirm which of the theoretical calculations is more suitable, we have carried out the experiments of the resonant X-ray emission spectroscopy (RXES) around the Fe Kβ emission lines for K4Fe(CN)6 and K3Fe(CN)6, in order to acquire the electronic structure of Fe atom as a model compound of hexacyanoferrate. In the RXES results of K4Fe(CN)6, three Raman scattering peaks are observed at 6.5, 9.5, and 15.4 eV near the elastic peak, respectively, called Raman Peak (RP) 1, RP2, and RP3. By comparing theoretical calculations of Raman scattering peaks of hexacyanoferrate [Y. Nanba: Doctoral Thesis, Okayama University, 2012 (in Japanese)], the Raman shift energies of RP1 were close to those of the metal-to-ligand charge transfer (MLCT). On the other hand, the Raman shift energies of RP3 were close to those of the ligand-to-metal charge transfer (LMCT). A similar result was also obtained in those of K3Fe(CN)6. It was found that the features of the MLCT excitation and the LMCT one were observed using the RXES experiments.