4d Photoabsorption Research Articles

Vibrational and ligand-field effects in the high resolution core-level spectroscopy of molecules

High resolution Si2p and Br3d core-level spectra of small molecules (photoabsorption, photoelectron and Auger) all show fine structure due to vibrational or ligand field splitting. The Si2p photoelectron and photoabsorption spectra of SiH 4, SiD 4 and Si 2H 6 show rich vibrational structure from both the symmetric and the asymmetric SiH(D) vibrational modes. The symmetric ν 1 vibrational mode dominates the photoelectron spectra of SiH 4 ( ν 1 = 2379 cm −1) and SiD 4 ( ν 1 = 1710 cm −1). In contrast, the asymmetric bending mode is more dominant in the photoabsorption spectra of the early Rydberg levels of SiH 4 and SiD 4 and completely dominant in both the photoelectron and photoabsorption spectra of Si 2H 6. In contrast, the core-level spectra of heavy elements such as Br and I are dominated by ligand field splitting. The high resolution Br 3d photoelectron spectrum of HBr shows the 3 d 3 2 doublet and 3 d 5 2 triplet characteristic of ligand field splitting. This same splitting is shown to dominate the previously recorded MVV Auger spectrum and the pre-edge Br 3d photoabsorption spectrum.

Determination of valence states in Fe3O4 by resonant photoemission

We report resonant photoemission measurements across the Fe 3p→3d photoabsorption threshold from the (110) surface of cleaved single-crystal Fe3O4 using synchrotron radiation. The resonant enhancement effect is used to distinguish the Fe 3d-derived states from the overlapping O 2p states in the valence band. The Fe 3d-derived states are found to extend about 18 eV below the Fermi level. Constant-initial-state spectroscopy across the Fe 3p excitation threshold reveals that this large valence bandwidth is due to a significant amount of cation–ligand hybridization; this result is in accord with recent configuration interaction cluster calculations of the photoemission final states in iron oxides reported by Fujimori et al. The electronic levels that are primarily associated with the different Fe2+ and Fe3+ cation environments in Fe3O4 are identified based on a comparison with photoemission spectra measured from cleaved FexO (x≂0.945) and α-Fe2O3 single crystals. Upon O2 adsorption, the Fe3O4(110) surface is rapidly oxidized, as evidenced by a decrease in the photoemission features associated with the Fe2+ valence state.

Valence Band Electronic Structure of Cleaved Iron Oxide Single Crystals Studied by Resonant Photoemission

AbstractSynchrotron radiation has been used to perform resonant photoemission measurements across the 3p→3d photoabsorption threshold from cleaved FexO (x ≃0.945), Fe3O4, and α-Fe2O3 single crystal surfaces. The resonant enhancement of the Fe 3d photoelectrons allows the Fe 3d-derived final states in the valence band to be distinguished from the overlapping O 2p states. Using well-characterized single crystals, the distributions of Fe 3d-derived states associated with the ferrous (Fe2+) and ferric (Fe3+) cations have been identified. The Fe 3d-derived states are found to extend about 18 eV below the Fermi level in each oxide, which can be attributed to a significant amount of hybridization between the Fe 3d and O 2p orbitals.

Decay of the giant 4d photoabsorption resonance in atomic Cs and Sm

The photoelectron spectra and the relative partial photoionisation cross sections of atomic Cs and Sm have been determined in the photon energy range of 4d-4f, epsilon f excitations (Cs50-130 eV; Sm 120-160 eV). For Cs direct 4d ionisation dominates whereas the Sm '4d to 4f, epsilon f resonance' mainly autoionises via the emission of a 4f electron. The Sm 4d partial cross section goes through a maximum about 12 eV above threshold, where it becomes comparable with the 4f partial cross section. The 4f type character of the Sm to excited wavefunction at threshold turns into 4f, epsilon f type character about 7 eV above. Close to the 4d threshold the 5s, 5p and two-electron satellite photoemission lines are strongly enhanced for both atoms.

The 4d Photoabsorption Spectra of La, LaF3, Ba and BaF2: Dependence on the Chemical and Structural Environment

The photoabsorption spectra associated with the excitation of 4 d electrons were measured for La, LaF 3 , Ba and BaF 2 . The line shape of the multiplet structures appearing at energies lower than the threshold shows that there is some interference between the discrete and continuum states. The spectra for BaF 2 has several small structures superposed on the broad absorption band, suggesting that neither 5 f or 6 f state is a completely continuum state. Both states are interpreted as the states hybridized with 1 P continuum states. The amount of the hybridization is found to be very sensitive to the valency and the crystal structure.

Photoabsorption by the 3d shell in Ce, Pr, Ho, and Er: Observations and calculations.

Improved 3d photoabsorption spectra of the series of rare-earth fluorides have been obtained by recording total electron yield and using monochromatized synchrotron radiation. They are compared with predicted spectra resulting from an average-of-configuration calculation of wave functions employing radial integrals adjusted to the observed spectrum in each case; results are presented here for Ce, Pr, Ho, and Er spectra. Improved resolution of the Ce spectrum permitted for the first time a determination of the proper scaling for all of the electrostatic parameters.

Discrete 4d photoabsorption spectrum of Ba^2+

The role of true collective effects in the 4d photoabsorption spectrum of Ba2+ is shown to be minor. The most significant departures from independent particle behavior are in fact due to correlations involving the 5p, not the 4d, shell; their importance is magnified by the delicate balance of opposing single-particle forces. Reevaluation of the ionization limit reveals the presence of Beutler–Fano structures in the experimental data, the first that have been observed for excitations underneath closed shells.

On the interplay between dielectric screening and core hole relaxation in soft X-ray absorption

A convenient approximate prescription for studying the interplay between dielectric polarisation effects and the relaxation of outer-shell electrons towards a deep core hole is tested for the case of 3d photoabsorption in xenon. The authors adapt the methods of Amusia and co-workers (1980) to a newly developed relativistic time-dependent local density approximation (RTDLDA). The natural choice of a Slater transition-state potential for the RTDLDA calculation produces nearly quantitative agreement with recent absolute cross section data.

3d photoabsorption in gaseous and solid xenon

The 3d absorption spectra of gaseous and solid xenon are compared. The spectrum of the gas agrees substantially with earlier data apart from two additional weak peaks about 1.3 and 5.0 eV above the M5 threshold. Comparison with the 3P1 and 3D1 lines in the absorption spectra of Ce4+, La3+, Ba2+ and Cs+ suggests that the weak xenon peaks represent transitions into resonantly localised continuum f states. No corresponding structure has been reported in the 4d spectrum. The gross structure of the spectrum of the solid is similar to that of the gas with the dominating M4 and M5 continuum peaks at the same energies and with similar cross sections. Notable differences are disappearance of the 1.3 eV peak, enhancement of the 5.0 eV peak and the appearance of weak maxima extending from 7.8 eV above the M5 threshold to higher energy, across both M4 and M5 continuum peaks. This structure, which lies above the range of existing density of states calculations, is attributed to scattering from surrounding atoms. No corresponding structure has been reported either in the 4d spectrum of solid xenon or in the isoelectronic M4,5 spectra of I-, Cs+, Ba2+ or La3+ in solids.

Photoabsorption and electron yields of La and Gd in the vicinity of the 3d thresholds

A comparative study of the 3d photoabsorption and electron-yield spectra of La and Gd using synchrotron radiation emitted by the Orsay storage ring (ACO) is presented. The effects of sample thickness on each kind of spectrum are discussed. The mean sampling depths for La and Gd are determined from the variations in intensity of the main excitation lines as a function of film thickness in the yield spectra. The advantages and potential of the yield technique for the study of lanthanide spectra are pointed out.

The Spectator electrons approximation in the 3d and 4s spectra of Cr I

The 3d and 4s photoabsorption spectra of Cr I have been observed by using the synchrotron radiation emitted by the Bonn 500 MeV electron accelerator as the source of background continuum. The resulting spectrum is unexpectedly simple, and this is explained within the spectator electrons approximation. The more intense transitions can be arranged in Rydberg series. A prominent series of transmission windows arises by double excitation. A detailed analysis is presented, supported by some ab initio Hartree-Fock calculations and also by comparison with the semi-empirical calculations of Roth (1970) which include mixing between all the (3d + 4s) 5 4p configurations.

The 3d photoabsorption of Tm 3+

The four lines predicted theoretically in Tm 3+ 3d photoabsorption are observed. By fitting the eigenvalues and the observed energies, new values of radial parameters are determined and it is shown that the configuration 3d 94f 13 in Tm 3+ is better described in j-j coupling.

Analysis of the atomic photoabsorption spectra of Rb and Sr based on the Z+1 approximation

The Z+1 approximation is discussed in connection with the final-state distribution of the Rb 3d photoabsorption spectrum. A method of calculating correction terms to the Z+1 energies is discussed. Also the Sr 3d photoabsorption spectrum is analysed and from this the atomic Sr 3d3/2, 5/2 ionisation energies are extracted (144.14(10) eV and 142.41(10) eV, respectively). In the light of recently reported core ionisation energies for Rb and Sr previous assignments in the 3p absorption spectra are also discussed.

Delayed onset of 4d photoemission relative to the giant 4d photoabsorption of La

For the giant 4d photoabsorption of La, both the total photoabsorption spectrum and the N 4.5-derived Auger emission intensity spectrum increase significantly above h ν ≅ 112 eV, with spectral peaks at h ν = 118 and 119 eV, respectively. However, the predominant 4d photoemission partial cross section shows a delayed onset of ∼ 4 eV, with a peak at h ν = 121 eV, while the 5s, 5p, and 5d partial cross sections all show a strong resonant enhancement at lower energies, with spectral peaks at h ν = 116.6 eV. These results are compared with a recent many-body calculation for Ce. The photon energy dependence of the La 4d 5 2 /4d 3 2 photo-emission branching ratio is consistent with a “final-state model.”

Continuum and discrete states in the 3d photoabsorption spectra of Xe-like ions

The 3d subshell photoabsorption spectra of the Xe-like ions I − , Cs + , Ba 2+ , and La 3+ in a number of ionic solids have been measured. The spectra exhibit two different kinds of structures (due to 3d-4f resonances and delayed maxima of the 3d-εf continuum) and indicate that the 4f orbits in the 3d 9 4f configuration have collapsed in Cs + and Ba 2+ .

Photoabsorption in the vicinity of 3d edges of Eu and Gd

Observations of the 3d photoabsorption spectra of isoelectronic Eu2+ and Gd3+ are reported. Their theoretical positions and relative intensities based on the 3d104f7 to 3d94f8 transition array are given and found to be in good agreement with the experimentally observed principal features. The 3d photoabsorption of the trivalent Eu is discussed and compared with that of trivalent Yb.

Giant dipole resonance in 4d photo absorption of atomic barium

We calculate the photoabsorption cross section for the 4d 10 and 5p 6 shells of atomic barium using the random phase approximation (RPAE) including relaxation. For both shells the oscillator strength goes mainly into a collective vibration of the entire shell.

Oscillator strengths for multiple ionization in the outer and first inner shells of Kr and Xe

Abstract Oscillator-strength spectra are reported for the formulation of the charge states one to four following N and M ionization in Kr and O and N ionization in Xe. The spectra were derived from coincidence measurements of small-angle inelastically scattered 10-keV electrons in the two gases and the ions formed. The spectra of Kr 1+ and Xe 1+ gave evidence of the presence of a minimum and subsequent maximum in the contribution of 4p-ed transitions in Kr and 5p-ed transitions in Xe. Our study further shows that simultaneous ionization in inner and outer shell of the type (3d,N) in Kr and (4d,O) in Xe behaves like a direct electron-interaction process. Its contribution is quite appreciable and cannot be neglected when one compares calculated 3d (or 4d) photoabsorption with experiment. For that purpose we present a number of separate subshell oscillator-strength distributions. The present results are compared with photoionization and absorption data. Their relation with our previous work on total single and multiple ionization of Kr and Xe by electron impact is discussed.