4d Photoabsorption Research Articles

An unusual Cu/Te hybridization in the Cu0.3ZrTe2 intercalation compound

The electronic structure of the novel intercalation compound Cu0.3ZrTe2 was analyzed using the X-ray photoelectron spectroscopy, resonant photoelectron spectroscopy and DFT calculations. The resonant photoemission enhancement of the valence band features of Cu0.3ZrTe2 at the Zr 3p→4d and Cu 3p→3d photo absorption thresholds was studied. The tetrahedral coordination of the Cu atoms by the Te atoms was shown to be responsible for the strong chemical bonding of the Cu atoms within the ZrTe2 lattice through the Cu 3d/Te 5p hybridization. These findings were confirmed by theoretical density of states (DOS) calculations performed for CuxZrTe2 (x = 0.25 and 0.5) with the Cu atoms tetrahedrally and octahedrally coordinated by Te atoms. It was concluded that the substitution of atoms in the CuxTiSe2 system with heavier and polarizable ones (Se→Te, Ti→Zr), i.e. an increase in the lattice polarizability, destabilizes the octahedral coordination of the Cu atoms by the Se/Te ones. This limits the stability of the phases characterized by quantum states with a charge density wave and superconductivity.

Photoemission studies on (1 1 1) textured Cr doped Eu2O3 thin film

The electronic properties of (1 1 1) oriented Cr doped Eu2O3 thin film has been studied using the x ray absorption and photoemission spectroscopic techniques. Cr-2p core level XPS and Cr-L edge XAS results confirm the 3+ ionic state of Cr, that precludes the formation of Cr metal clusters in the film. The modification in the electronic structure due to Cr doping is probed by the resonant photoemission spectroscopy measurements using variable photon energy sources at Eu 4d → 4f and Cr 3p → 3d photo absorption region. The valence band spectra (at 145 eV) shows drastic change in the intensity of feature close to Fermi level along with an additional feature in Cr doped film when compared with the valence band spectra of the undoped film.

Electronic structure studies of Fe doped Eu 2 O 3 thin film using x-ray absorption and resonant photoemission spectroscopy

Herein, we have investigated the electronic properties of Fe doped Eu2O3 thin film using x-ray absorption spectroscopy (XAS), valence band spectroscopy and resonant photoemission spectroscopy (RPES). The Fe L3, 2 edge XAS spectra confirms the “3+” ionic state of the Fe in the film. The valence band spectrum of Fe doped film shows an enhancement in the intensity of feature “A” close to Fermi level and origin of another feature “E” at 11.1 eV. The valence band spectroscopy measurements have been performed at the energies in the Eu 4d → 4f and Fe 3p → 3d photo absorption region that clearly disentangles the features in valence band to be of either Eu and Fe hybridized with O or to be of Eu and O only.

Theoretical study of the 4d photoabsorption of the Cs+ ion

Calculations of the 4d absolute photoabsorption cross sections of the Xe-like Cs+ ion covering the energy region from 80 to 190 eV have been performed by using the multi-configuration Dirac–Fock method. The calculated cross sections are compared with the absolute experimental photoabsorption cross-section spectrum (Kjeldsen et al 2002 J. Phys. B: At. Mol. Opt. Phys. 35 2845) and other available theoretical results. In the 80–90 eV region, the discrete structure resulting from photoexcitation of a 4d electron into nf and np orbits are successfully identified. Above the 4d threshold, i.e. in the 90–190 eV energy region, a reasonable agreement between experiment and computations is found for the intense 4d → εf shape resonance.

Redistribution of Ce 4d oscillator strength observed in photoionization of endohedral Ce@C+82 ions

Cerium atoms and ions with a filled 4d subshell are expected to have a 4d photoabsorption oscillator strength of 10 according to the number of equivalent electrons in that shell. While this expectation was confirmed for free atomic cerium ions by observing the single and double photoionization channels, measurements with Ce ions encapsulated within a C82 Fullerene cage showed that the single and double ionization channels contain far less than 50% of the Ce 4d oscillator strength.

4d photoabsorption spectra of Indium (In II–In IV)

The 4d photoabsorption spectra of singly to triply ionized indium have been recorded using the dual laser plasma technique in the 24.5–55 eV photon energy range. The data substantiate and add to previously classified lines in In II and In IV while many new lines are tentatively identified in In III. Transitions were assigned with the aid of Hartree–Fock calculations.

4d photoabsorption spectra of Sn II and Sn IV in the 30–65 eV region

EUV photoabsorption spectra of tin ions Sn II and Sn IV have been recorded using the dual laser-produced plasma (DLP) technique in the 30–65 eV region. It is known from previous studies by Lysaght et al (2005 Phys. Rev. A 72 014502), in the 30–100 eV domain, that gradual 4f contraction along the isonuclear sequence of Sn I through Sn IV results in a redistribution of the oscillator strength from the continuum to the pseudo-discrete 4d → f channels, with many intense absorption lines dominating the spectra of Sn IV. Using Hartree–Fock with configuration interaction calculations allows us to successfully account for, and permits identification of, pseudo-discrete 4d → np, nf features within the spectra of Sn II and Sn IV.

Cs 3d absorption and resonant photoemission study of caesium halogenides

The highly localized 4f electrons play an important role in forming of the electronic structure and properties of compounds. The 3d photoabsorption and resonant decay spectra of Cs halides represent an interesting case showing both the localized and spatially extended f wavefunction features. We present and discuss the Cs 3d x-ray absorption and resonant photoelectron emission spectra of the Cs halides. The Cs 3d absorption spectra exhibit a strong atomlike shape resonance behavior, solidstate effects play a minor role. The appearance of the spectral features, which are intrinsic to a localized state, in the decay spectra show that the Cs 3d photoelectron, temporally and spatially trapped in the Cs 3d shape resonance due to the potential barrier for εf electrons near threshold, has substantially localized nature.

Discrete structure in the 4d photoabsorption spectra ofCs III, Cs IV and Cs V

XUV photoabsorption spectra of caesium, in ion stages up to Cs4+, have been obtained experimentally with the dual laser-produced plasma technique. From the results it can be inferredthat the 4d photoabsorption cross-section changes dramaticallyin appearance along the isonuclear sequence Cs throughCs4+. While the spectra of Cs, Cs+ and Cs2+ aredominated by a giant dipole 4d →εfresonance, discrete structure, which essentially increases inintensity with increasing ion stage, is also present below threshold. Between Cs2+ and Cs3+ much of the oscillator strength is abruptly transferred from the continuumto the discrete spectrum so that a few intense broad featuresdominate the spectra of Cs3+ and Cs4+. Multiconfiguration Hartree-Fock calculations successfullyaccount for this behaviour and permit identification of thediscrete features.

The evolution of 4d photoabsorption in Sb with increasing ionization

The photoabsorption spectra of Sb+, Sb2+, Sb3+ and Sb4+ have been obtained in the XUV spectral region with the dual laser-produced plasma (DLP) technique. Photoexcitation from the 4d subshell is the dominant process in the 30-100 eV energy region. In Sb+, for photon energies between 30 and 50 eV, discrete structure corresponding to 4d np, n1f (n5,n14) transitions is obtained, while above 50 eV the spectrum is dominated by an intense 4df resonance. Apart from the 4d5p transitions the features are very weak. The 4df resonance is still observed in Sb2+ as the dominant feature in the spectrum, but in Sb3+ and Sb4+ there is significant transfer of oscillator strength from the continuum to the discrete spectra, in particular to the 4d nf transitions. This behaviour mirrors the effects of contraction of the 4f wavefunction, which is seen to be more gradual here than in elements with Z>54. Multiconfiguration Hartree-Fock and time-dependent local density approximation calculations successfully reproduce this behaviour.

Discrete structure in the 4d photoabsorption spectrum of antimony and its ions

The 4d inner-shell absorption spectra of Sb, Sb+, Sb2+ and Sb3+ have been obtained with the dual-laser-produced plasma technique. Discrete structure has been observed in the 30-40 eV region and identified as originating from 4d-5p transitions by comparison with the results of Hartree-Fock calculations performed within the superposition of configurations method. For comparison of theoretical and experimental spectra, 4d photoabsorption cross sections were calculated which took non-radiative decay rates into account. It was found to be necessary to include absorption from excited states of the ground configurations, especially in the higher ionization stages. Synthetic spectra, which allowed for thermal lower state population distributions, were produced and these are in agreement with the experimental data.

Ni 2p–3d photoabsorption and strong charge transfer satellites in divalent Ni complexes with molecular ligands. Evaluation of π-back donation based on the density functional theory approach

Abstract Density functional theory within a transition potential approach (DFT-TP) is applied to interpret remarkably strong π-type MLCT (metal-to-ligand charge transfer) satellites in the Ni 2p photoabsorption of planar low-spin Ni II complexes, K 2 Ni(CN) 4 ·H 2 O and bis(dimethylglyoximato)nickel. The MLCT intensities calculated with DFT-TP are in good agreement with experiment, whereas the HF-STEX (Hartree–Fock-based static exchange approximation) approach underestimates the intensities. The DFT-TP approach gives more reasonable π-back donation due to a better description of the strong covalency hybridization of the ligand π* orbitals with the occupied 3d orbitals. The DFT analysis indicates that we can evaluate π-back donation qualitatively by experimentally examining the MLCT satellites.

Discrete structure in the 4d photoabsorption spectrum of tellurium and its ions

The 4d inner-shell absorption spectra of Te, Te+, Te2+ and Te3+ have been recorded with the dual laser produced plasma technique. Discrete structure due to 4d5p transitions has been observed in the 37 - 45 eV region and identified using Hartree-Fock calculations within the superposition of configurations method. For comparisons of theoretical and experimental spectra, the method approximates a calculation of the resonant part of the photoionization cross section. It was also necessary, especially in the higher ion stages, to include absorption from excited states of the ground configurations. From these, synthetic spectra were produced which generally agree well with the experimental data.

Spin-resolved core-level and valence-band photoemission spectroscopy of ferromagnetic MnAs

Abstract Spin-resolved core-level and valence-band photoemission spectroscopy of a MnAs single crystal has been done. The spin-polarization spectra of the Mn 3p and As 3d core levels have structures, indicating spin-polarized photoemission from these states. The minority-spin spectra of Mn 3p and As 3d have stronger intensities at lower binding energy. The Mn 3p majority-spin spectrum has a broader width than the Mn 3p minority-spin spectrum. The spin polarization of valence-band photoemission spectra is enhanced in the Mn 3p–3d photoabsorption region, indicating spin-dependent interference effects.

The Location of 4d Photoabsorption Resonances and theCollapse of 4f Radial Wavefunction in Lanthanides

Using the spin-polarised method it is shown that the collapse ofwavefunctions of the 4fN shell in free lanthanideatoms for the upper terms of the excited4d94fN configuration is completed, notat the beginning, but in the middle of the lanthanum group. This isthe reason for the redistribution between photoionization andphotoexcitation processes and for the shift of the giant resonancethrough the 4d ionization limit when passing over from Eu toGd.

3d Photoabsorption in Zn II, Ga III and Ge IV

The 3d photoabsorption spectra of Cu I-like Zn II, Ga III and Ge IV have been recorded in the 25-100 eV region using the dual laser plasma technique. The spectra are dominated by transitions of the type which have been identified by comparison with multiconfiguration Hartree-Fock calculations.

Discrete structure in the 4d photoabsorption spectrum of

The photoabsorption spectrum of Xe-like has been obtained in the XUV spectral region with the dual-laser-produced plasma (DLP) technique. Photoexcitation from the 4d subshell is the dominant process in the 80 - 150 eV energy range and is intermediate in behaviour between the well documented cases of Xe and . Between 80 and 90 eV discrete structure, corresponding to transitions is obtained, while above 90 eV the spectrum is dominated by an intense resonance. Multiconfiguration Hartree - Fock (MCHF) calculations facilitated identification of the majority of the features observed.

High-resolution photoabsorption and photoelectron spectra of bromine-containing molecules at the Br 3d edge: the importance of ligand field splitting

Using monochromatic synchrotron radiation, we have recorded high-resolution Br 3d photoelectron and photoabsorption spectra (PES and PAS, respectively) for the five molecules: HBr, DBr, and . The Br 3d PES of HBr, DBr and show five peaks due to the combined effects of ligand field (or molecular field) and spin - orbit splitting. The and PES are vibrationally broadened, but also show additional broadening from ligand field splitting. The Br 3d ligand field splittings (as quantified by the crystal field parameter) are similar to the I 4d values for the iodine analogues, and increase in the order of . The Br 3d binding energies also increase in the above order due to the increasing electronegativity of the substituents. The very complex Br 3d photoabsorption spectra also show the same ligand field/spin - orbit splitting which split each transition into five transitions. These spectra are dominated by the peaks from the five transitions; but a myriad of other peaks from the (n = 4, 5), np (n = 6 - 9), ns (n = 6, 7) and nf (n = 4, 5) transitions are required to fit these spectra. Good fits to all the spectra have been obtained using ligand field splittings which are similar to the PES results, and quantum defects for s, p, d and f orbitals of , 1.6 - 2.0 and 0.8 - 1, respectively.

Magnetic circular dichroism in 4d→4f resonant photoemission and photoabsorption of Gd metal

A consistent description of magnetic circular dichroism (MCD) in resonant 4d\ensuremath{\rightarrow}4f photoemission (PE) and 4d photoabsorption (PA) from magnetized rare-earth metals is presented. In the case of ferromagnetic Gd metal it is found that the MCD of the resonant 4fPE spectra varies strongly when the photon energy is scanned across the resonance region. We show that the spectral shape of the 4fPE multiplet is determined by the total angular momentum of the intermediate ${4\mathrm{d}}^{9}$ ${4\mathrm{f}}^{8}$ PA state, which is reflected in the sign of the PA-MCD at the excitation energy.

Discrete structure in the 3d photoabsorption spectra of neutral, singly ionized and doubly ionized bromine.

The 3d photoabsorption spectra of Br, ${\mathrm{Br}}^{+}$, and ${\mathrm{Br}}^{2+}$ have been recorded photographically in the 60--90 eV region using the dual-laser-produced plasma technique. In each case intense 3d\ensuremath{\rightarrow}4p transitions were observed while 3d\ensuremath{\rightarrow}np (n\ensuremath{\gtrsim}4) features were also obtained in the spectrum of neutral bromine. The transitions were classified with the aid of multiconfiguration Hartree-Fock calculations. The excited states are predicted to decay by direct autoionization involving 4s or 4p electrons and the rates for the different processes and resulting linewidths were also calculated. From these data theoretical cross sections for the observed features were also computed. \textcopyright{} 1996 The American Physical Society.