Resonant Photoelectron Spectra Research Articles

Resonant auger spectra of TiO2 at Ti2p and O1s absorption edges

Abstract Resonant Auger measurements of TiO 2 (anatase have been performed at the Ti 2p and O 1s X-ray-absorption edges. The resonant photoelectron spectra excited at the Ti 2p absorption maxima show a strong resonance enhancement of the valence band photoemission intensity indicating the strong hybridization of the Ti 3d-level with the anion valence band. The degree of localization of the excited 3d electron in intermediate and in final Auger ionic configurations, and its influence on the decay spectra is discussed. In contrast, the resonant photoelectron spectra excited at the O 1s absorption maxima do not show resonance enhancement of the valence band which indicates that the absorption spectrum is formed by the delocalized states.

Molecular inner-shell spectroscopy of planar Ni complexes

Abstract Remarkably strong charge transfer bands due to excitations to unoccupied ligand orbitals are found in addition to the lowest atomic-like Ni 2p–3d* transitions in Ni 2p photoabsorption spectra of planar Ni(II) molecular complexes with low-spin 3d8 configurations, hydrated and anhydrous K2Ni(CN)4 and bis(dimethylglyoximato)Ni(II). Spectral features are characterized by examining the polarization dependence of single crystals. Resonant photoelectron spectra in the Ni 3s, 3p and 3d regions were investigated through the Ni 2p excitations. A number of satellite series, which are weakly observed or absent in the off-resonant photoelectron spectra, are enhanced through the resonant excitation for both the samples. The enhanced satellite bands lower the electron kinetic energy with increase of the photoexcitation energy and converge to the normal Auger lines at the Ni 2p ionization threshold. This behaviour is characteristic of one-electron states in molecular solids.

Resonant behavior of satellite photoelectrons in the Ni 3p and 3s region at the Ni 2p excitation of K 2Ni(CN) 4

Resonant Ni 3p and 3s photoelectron spectra were measured at the Ni 2p edge for anhydrous K 2Ni(CN) 4 complex. A number of satellite series, which are mostly forbidden in the non-resonant spectrum, become strongly observable via the resonant excitations. Each satellite lowers its kinetic energy for the higher resonance energy, showing a one-to-one correspondence with the Ni 2p 3/2 and 2p 1/2 resonantly excited states. This behavior manifests a one-electron feature in the core excitons, where electrons are bound by the singly and doubly charged states in the intermediate and final states, respectively, and is characteristic of molecular systems in solids such as Ni(CN) 4 2−.

Ni 2 p resonant photoelectron spectra of some planar nickel complexes

Resonant photoelectron spectra in the Ni3 s,3 p and3 d regions were investigated at the Ni2 p edge for the planar nickel complexes K 2Ni(CN) 4 and bis-(dimethylglyoximato)nickel(II). A number of satellite series, which are observed weakly or are absent in the off-resonant spectra, are enhanced through the resonant excitation for both samples. The enhanced satellite bands lower the electron kinetic energy with increasing photoexcitation energy and converge to the normal Auger lines at the Ni2 p ionization threshold. Furthermore, the electron kinetic energy dependence on the photon energy is different between these complexes. This behavior is characteristic of one-electron exciton states in molecular solids.

Ni L-Edge Absorption Structure of K2Ni(CN)4Ionic Solid Investigated with Resonant Photoelectron Spectroscopy

Resonant photoelectron spectra of the K2Ni(CN) 4 ionic solid following the Ni 2p photoabsorption were measured to interpret the L-edge absorption spectrum. [Ni(CN)4] 2- is a square-planar complex ion and its absorption spectrum shows rather complicated resonance features in comparison with those of nickel oxide and nickel dihalides. In the resonant photoelectron spectra, all the peaks enhanced by resonant photoabsorption have higher kinetic energies than the normal Auger peaks and are attributable to spectator Auger transitions. It is clearly observed that the kinetic energies of all the spectator Auger electrons decrease with increase of the photon energy in the Ni 2p3/2 photoexcited region. The kinetic energy dependence observed is reasonable assuming that the Ni L-edge resonance absorptions are exciton-like and excited electrons are shaken up with high probability.

Resonant inner-shell photoelectron spectra of ground-state and laser-excited Cr atoms

Photoelectron spectra and partial cross sections of ground-state and laser-excited Cr atoms in the range of the excitations are presented. The experimental spectra are compared with results obtained by calculations within the spin-polarized random-phase approximation with exchange (SP RPAE), in which the dynamic relaxation upon core hole creation is taken into account.

3d-Resonant photo- and auger emission of Ce in CeO 2

The Ce 3d-edge resonant photoelectron and Auger electron emission spectra in CeO 2 have been measured. The 4s-, 4p- and 4d-emission at off-resonance excitations consists of two parts separated by about 13 eV, which correspond to different final-state configurations. The resonantly excited spectra show the different nature of the M 45-main and satellite photoexcitations. The satellites seem to correspond to intermediate states of a more extended character. For M 45N 45N 45 on-resonance decay the most interesting finding (obtained by comparison with the relevant spectra of Ce in CeCl 3 and La in LaF 3) is the considerable suppression of the high energy band related to the upper levels of the 4d 84f n final state configurations. The M 45N 45N 45 decay in CeO 2 appears to be more similar to the situation in metallic cerium than in the insulating CeCl 3.

2p-3d resonant Auger scattering by K+ ions of KMnF3 without the influence of the crystal-field splitting.

The 2p-3d resonant photoelectron and Auger spectra of ${\mathrm{K}}^{+}$ in ${\mathrm{KMnF}}_{3}$ have been measured. Contrary to the case of ${\mathrm{K}}^{+}$ in KCl studied by Elango et al. [Phys. Rev. B 47, 11 736 (1993)], the crystal field at ${\mathrm{K}}^{+}$ sites is very weak in ${\mathrm{KMnF}}_{3}$ and the 3d orbital of ${\mathrm{K}}^{+}$ is barely split into the ${\mathit{t}}_{2\mathit{g}}$ and ${\mathit{e}}_{\mathit{g}}$ components. It is shown that at the resonance a spectator structure which originates from the 3${\mathit{p}}^{\mathrm{\ensuremath{-}}2}$3d final configuration of ${\mathrm{K}}^{+}$ is strongly enhanced in the ${\mathit{L}}_{2,3}$${\mathit{M}}_{2,3}$${\mathit{M}}_{2,3}$ Auger spectra. This structure shifts to higher kinetic energy linearly with increasing photon energy, indicating the Auger-resonant inelastic-scattering character of the excitation-deexcitation process. The effect does not depend on the crystal-field splitting of the 2${\mathit{p}}^{5}$3d configuration, the intermediate configuration of this process.

Resonant photoemission versus incoherent superposition of Auger and photoemission signals

The angle-resolved resonant photoelectron spectra of Ni and Ce metals are reported. On M III resonance, the intensity of the 6-eV satellite of Ni is found to be independent of the angle of emission relative to the ▪-vector of the exciting light, while the valence-band photoemission (PE) intensity follows a cos 2 behavior as expected for PE. In contrast to Ni, the enhanced Ce4f PE signal on N IV,V resonance also varies according to cos 2. This shows that the resonant enhancement of the 6-eV Ni satellite is mainly due to a secondary Auger decay, whereas in case of the Ce4f signal it reflects resonant photoemission.

Resonant photoelectron spectra of Gd compounds

4f resonant photoelectron spectra of three kinds of Gd compounds, GdB 6, GdB 4 and Gd 2S 3, have been measured in the excitation photon energy from 32 to 154 eV. The line shapes of the 4f state of these materials are different from one another. The origin of the difference is discussed.

Photoelectron spectroscopy of MoS 2 at the sulfur 2p absorption edge

The sulfur 2p absorption edge and valence-band resonant photoelectron spectra of molybdenum disulfide (MoS 2), obtained using synchrotron radiation, are compared to the Mo4p edge results from previous work. A pre-edge feature in the S2p data shows transitions to unoccupied, dominantly Mo4d anti-bonding levels, indicating that significant covalent interactions exist between Mo and S valence orbitals. Resonant enhancement of valence-band photoelectron shake-up peaks is observed at the S2p → Mo4d excitation energies, while the sulfur ( L 2,3 VV) Auger peak dominates the spectrum when the S2p ionization threshold is reached. Anti-resonant intensity modulation of main valence band peaks is observed at photon energies corresponding to the S2p → Mo4d pre-edge feature. The results show that the principal decay channel after the S2p → Mo4d excitation leads to the enhancement of final states having S(3p) 4 Mo(4d) 3 electron configurations.

Decay of the Xe 4d to np excitations: resonant shake-off versus shake-up and spectator transitions

Resonant photoelectron spectra were measured in the photon energy range of Xe 4d to np excitations to study multielectron processes associated with the decay of these resonances. The results show a large fraction of shake-off electrons in the total decay rate and indicate an increase of this fraction with increasing principal quantum number n of the photoexcited electron. Higher resolution measurements reveal that this increase accompanies a decrease in the corresponding probability for shake-up transitions. The consequences of this behaviour regarding double excitations and double Auger decay above the 4d ionisation threshold are discussed.

Resonant vacuum-ultraviolet photoelectron spectra of aligned Li atoms.

A new method is described in which Li atoms are excited and aligned by pumping of the Li $1{s}^{2}2s^{2}S_{\frac{1}{2}}\ensuremath{\rightarrow}1{s}^{2}2p^{2}P_{\frac{1}{2},\frac{3}{2}}$ transitions with a linearly polarized dye-laser beam, and subsequently raised to core-excited $1snl{n}^{\ensuremath{'}}{l}^{\ensuremath{'}}^{2}S$, $^{2}P$, $^{2}D$ states by linearly polarized synchrotron radiation. The intensity of the electrons ejected upon the Li $1snl{n}^{\ensuremath{'}}{l}^{\ensuremath{'}}^{2}S$, $^{2}D\ensuremath{\rightarrow}1{s}^{2}^{1}S_{0}\ensuremath{\epsilon}l$ autoionization strongly varied with the character of the core-excited state, the intermediate $^{2}P_{\frac{1}{2}}$ or $^{2}P_{\frac{3}{2}}$ state, and the angle between the polarization vectors of the two photon beams.

Photoemission study of Kr 3d-->np autoionization resonances.

Resonant photoelectron spectra of Kr have been taken in the photon-energy ranges of the 3d/sub 5/2/..-->..5p,6p and 3d/sub 3/2/..-->..5p excitations. The spectra, which closely resemble normal Kr/sup +/ 3d/sup -1/ Auger spectra, illustrate the importance of ''spectator'' Auger-like decay for inner-shell resonances, in which the initially excited electron does not participate in the core-hole deexcitation process, except to respond to the change in the atomic potential. Possible assignments for some of the spectator decay channels are discussed based on photoemission intensity measurements at the different 3d resonances. These assignments suggest that shake-up (e.g., 5p..-->..6p) of the ''spectator'' electron during the decay process is not quite as important as previously suspected. The resonance profiles of some of the more intense satellites have been determined over the 3d..-->..np resonances. Very small resonance effects also were observed in the partial cross section for 4p subshell ionization, which produced asymmetric Fano-type profiles. The 4p angular distribution, in contrast, exhibits a pronounced effect in the resonance energy range. The 4p results demonstrate that nonspectator autoionization also is present.

Orbital-collapse effects in photoemission from atomic Eu.

Resonant photoelectron spectra of atomic Eu have been measured in the photon-energy ranges of the ''4d..-->..4f '' (110-170 eV) and 3d..-->..4f (1120-1165 eV) excitations. For the ''4d..-->..4f '' giant resonance, the decay process results mostly in Eu/sup +/ main-line configurations, including some fractional enhancement directly into the 4d continuum. The 3d..-->..4f excitations, however, are characterized by competition between the main-line decay channels and channels corresponding to highly excited (satellite) ionic states. We find that decay after 4d excitation leads predominantly to the 4f continuum, whereas several channels participate in the decay following 3d excitation. The observed decay characteristics are discussed with regard to orbital-collapse phenomena.

Decay channels of the discrete and continuum Xe 4d resonances.

Excitations of the Xe 4d subshell to discrete np and continuum \ensuremath{\epsilon}f states have been studied by photoemission. The resonant photoelectron spectra provide the first direct evidence that the emission of continuously distributed shakeoff electrons is one of the dominant decay modes of the 4d\ensuremath{\rightarrow}np resonances. The same effect is proposed to account for the missing 4d intensity in the 4d\ensuremath{\rightarrow}\ensuremath{\epsilon}f shape resonance compared to the absorption cross section. The fraction of direct recombination in the decay of the 4d\ensuremath{\rightarrow}np resonances was determined quantitatively by partial cross-section and branching-ratio measurements of the 5s and 5p main lines in the photon-energy range from 60 to 70 eV. The modified Fano theory for partial cross sections was applied to nearly Lorentzian-type profiles in order to derive partial decay widths. The decay into the 5s and 5p photoemission channels amounts to less than 0.5% of the total decay rate. The 5${p}_{3/2}$:5${p}_{1/2}$ branching ratio was measured over a broad range (17--140 eV) in order to test details of relativistic random-phase approximation calculations concerning intershell correlations between the 4d and 5p subshells.

Photoreactions of Small Organic Molecules V. Absorption‐, Photoion‐ and Resonancephotoelectron‐Spectra of CF3Cl2, CF2Cl2, CFCl3 in the Energy Range 1025 eV

AbstractThe absorption spectra, photoion spectra, and resonance photoelectron spectra of CF3Cl, CF2Cl2, and CFCl3 have been measured in the energy range from 9 eV to 25 eV, ‐ Absolute cross sections of absorption are given. The stability of the parent ions decreases with increasing symmetry of the parent molecules. The fragment ions have been analyzed. Besides photocations, atomic chlorine and fluorine, fluoride and chloride are formed. The decay mechanisms are discussed, spectra are influenced by autoionization. The resonance photoelectron spectra reveal some new ionization potentials at high excitation energies.

Resonance photoelectron spectroscopy from autoionization states of CH3I

Abstract Resonance photoelectron spectra of methyl iodide have been taken by exciting individual autoionizing Rydberg states, and measuring the ejected electron energies by a time of flight technique. A number of spectra were obtained from autoionization states which are members of two series, converging respectively to the 2E 1 2 (ν = 0) and 2E 1 2 (ν2 =1) states of the ion. In addition to observing vibrational bands not previously reported, we found that the peak intensities are consistent with Bardsley's formulation of the configuration interaction theory of autoionization.

Photoelectron studies of boron compounds. Part 3.—Complexes of borane with Lewis bases

He(I) resonance photoelectron spectra are presented for the borane complexes of ammonia, mono-, di- and tri-methylamine, carbon monoxide and phosphorus trifluoride. The spectra are assigned by correlation with each other, with the spectra of the free bases, and with calculations. Agreement with calculations is good, and evidence is presented in favour of a simple Lewis donor-acceptor bond in the compounds, with some additional “back donation” in the carbon monoxide and phosphorus trifluoride complexes.

The photoelectron spectra of nitrogen trifluoride and nitrogen oxide trifluoride, and a reassignment of the spectra of tetrafluorides of group IV

The He (I) resonance photoelectron spectra of nitrogen trifluoride and nitrogen oxide trifluoride are presented, assigned, and correlated with boron trifluoride and carbon tetrafluoride spectra. The NF 3ONF 3 correlation is discussed in terms of a donor N bond in ONf 3, and from the ONF 3CF 4 correlation it is proposed that the highest occupied orbital in CF 4 is 1t 1. Correlations with MO calculations are discussed.