Chikara Sugiura

Sulfur K x‐ray absorption spectra of FeS, FeS2, and Fe2S3

The K absorption spectra of sulfur in FeS, FeS2 (pyrite), and Fe2S3 have been measured with a 50 cm bent‐quartz‐crystal vacuum spectrograph. The spectra of FeS and Fe2S3 are similar to each other but are fairly different from that of FeS2. The FeS2 spectrum is discussed in terms of two theoretical calculations: the energy band for FeS2 (pyrite) and the molecular orbital (MO) of the S22− ion. The spectra for FeS and Fe2S3 are explained by the application of Terakura’s theory and the first absorption band is attributed to the transitions to the empty antibonding states formed by the redistribution of the sulfur 3p bands under the influence of the iron 3d bands.

X‐ray absorption near‐edge structure of complex compounds (NH4)3RhCl6, K3RuCl6, and Ru(NH3)6Cl3

X‐ray absorption spectra of chlorine K edge, ruthenium LIII edge, and rhodium LIII edge from (NH4)3[RhCl6], K3[RuCl6], and [Ru(NH3)6]Cl3 have been measured with a Johann‐type 50 cm bent crystal vacuum spectrograph. The white lines due to the transitions to the incompletely filled antibonding molecular orbital (MO) 2t2g(π*) or nonbonding orbital t2g and the empty antibonding MO 3eg(σ*) for the octahedral complexes have been observed in the Cl K edge, Ru LIII edge, and Rh LIII edge regions. It is found that the two absorption peaks at the Ru LIII edge reflect the ligand‐field effect. An interpretation for experimental results of the Cl K edge and the Ru LIII edge absorption spectra in K3RuCl6 on the basis of the MO scheme leads us to the conclusion that the white lines at the Cl K edge suffer from the effect of core hole.

Sulfur-K X-Ray Spectra and Electronic Structure of a Semiconductor Ag2S

The Kβ emission and K-absorption spectra of sulfur in Ag2S are carefully measured and compared with the sulfur Kβ emission and K-absorption spectra of Cu1.8S reported previously. The spectra of Ag2S clearly show the existence of the energy gap in semiconducting Ag2S in contrast to the metallic phase Cu1.8S where the Kβ band edge overlaps with the K absorption edge. The sulfur-Kβ emission spectrum of Ag2S consists of two prominent peaks. The intensity of the high-energy peak is much greater than that of the low-energy peak, contrary to the sulfur-Kβ emission spectrum of Cu1.8S. It is suggested that the bottom of the conduction band of Ag2S arises mainly from the sulfur 4p states.

Iron K x‐ray absorption‐edge structures of FeS and FeS2

The Fe K absorption‐edge structures of the NiAs‐type FeS and the pyrite‐type FeS2 have been measured with a high‐resolution two‐crystal spectrometer. The K absorption edges consist of a step‐like structure and are interpreted in terms of the energy‐band structures for these sulfides. The presence of the absorption structure is much clearer in Fes2 than in FeS. This difference is attributed to the difference of the iron 3d states in FeS and FeS2 and the distortion of the octahedron [FeS6]10− in these sulfides. The Fe K absorption spectrum of FeS2 is compared with the sulfur K absorption spectrum reported previously and a good agreement is obtained between them.

K x‐ray absorption spectra of chlorine in 3d transition‐metal complexes

The chlorine K absorption spectra from MnCl2⋅4H2O, FeCl2⋅nH2O, CoCl2⋅6H2O, NiCl2⋅6H2O, and CuCl2⋅2H2O have been investigated using a 50 cm bent‐quartz crystal vacuum spectrograph. Chemical shifts are found for the first absorption maximum and discussed in relation to the d‐electron affinities of the divalent metal ions. The first maxima are attributed to the transitions from the chlorine 1s level to the empty antibonding orbitals originating mainly from the metal 3d and chlorine 3p orbitals. The other absorption structures are alike through five different hydrated dichlorides and are ascribed to the core‐level‐to‐empty‐state transitions in the Cl− ion. The present spectra are compared with those of the anhydrous metal dichlorides MCl2 (M = Mn, Fe, Co, Ni, and Cu) reported previously. It is illustrated that the first peaks are varied little by changing the anhydrides into the hydrates, but the other structures are considerably altered.

Palladium Liii x‐ray absorption‐edge structures of K2PdCl6, K2PdCl4, (NH4)2PdCl4, and trans‐[Pd(NH3)2Cl2]

The palladium Liii absorption spectra of complex compounds K2PdCl6, K2PdCl4, (NH4)2PdCl4, and trans‐[Pd(NH3)2Cl2] have been measured with a 50 cm bent‐quartz crystal vacuum spectrograph. A strong ‘‘white line’’ has been found at the absorption threshold and a few weak structures have been observed in the energy range of about 20 eV above the white line. These absorption structures have been interpreted in terms of molecular‐orbital (MO) theory. The Pd Liii absorption spectrum of trans‐[Pd(NH3)2Cl2] is somewhat different from those of K2PdCl4 and (NH4)2PdCl4 which are quite alike. The white line of K2PdCl6 shifts by 2.0 eV toward higher energies relative to that of K2PdCl4 or (NH4)2PdCl4. This chemical shift is due to the difference of the oxidation states of the palladium ions Pd2+ and Pd4+.

Chlorine K x‐ray absorption spectra from CrCl3 ⋅ 6H2O and FeCl3 ⋅ 6H2O

Chlorine K x‐ray absorption spectra are reported in CrCl3 ⋅ 6H20 and FeCl3 ⋅ 6H20 crystals. A new feature in the Crd3 ⋅ 6H20 spectrum the splitting of 3d levels of Cr3+ ion in the crystal field of CrCl3 ⋅ 6H20. The white lines in the spectra are discussed. (AIP)

Influence of ligands on the x‐ray absorption near‐edge structure of palladium(II) complex compounds

The palladium LIII absorption and chlorine K absorption spectra from [Pd(NH3)4]Cl2 ⋅ H2O and Pd(OCOCH3)2 have been reported for the first time and discussed in connection with the Pd LIII absorption and Cl K absorption spectra of K2PdCl4, reported previously. The influence of the ligands Cl−, OCOCH−3, and NH3 has been observed in the pallaldium LIII absorption spectra of these compounds. The observed chemical shift of a strong ‘‘white line’’ at the Pd LIII absorption threshold can be explained in terms of the spectrochemical series of the ligands. An intense white line disappears at the Cl K absorption threshold of [Pd(NH3)4]Cl2 ⋅ H2O in contrast to the Cl K absorption spectrum of K2PdCl4.

X‐ray spectra and electronic band structures of PdCl2 and CdCl2

The Pd Lβ2,15 emission, Pd LIII absorption, Cd Lβ2,15 emission, Cd LIII absorption, Cl Kβ emission, and Cl K absorption spectra of PdCl2 and CdCl2 have been obtained with a 50−cm bent−quartz−crystal vacuum spectrograph. The electronic band structures are determined empirically from the emission and absorption spectra. The valence band of PdCl2 consists of the overlap of the 4d band of palladium and the 3p band of chlorine; the upper part arises primarily from the d band and the lower part predominantly from the p band. In CdCl2 the valence band consists of the 3p band of chlorine and the bottom of the conduction band arises from the empty 5s state of the Cd++ ion. A tentative interpretation for the Pd LIII, Cd LIII, and Cl K absorption spectra is made in terms of the core−level−to−band transition. It is indicated that the chemical bonds of these metal chlorides are largely covalent.

Multiple-scattering calculation of sulfur K x-ray absorption spectra for FeS, CoS and NiS

Abstract Sulfur K X-ray-absorption near-edge-structures (XANES) are calculated for the first time for NiAs-type FeS, CoS and NiS crystals having a hexagonal structure from a multiple-scattering approach within a muffin-tin approximation. Comparison between the calculated and experimental results indicates that a core hole created in the absorbing S atom does not so strongly affect the S K XANES of the metallic phase FeS, CoS and NiS.