The He(I) photoelectron spectra of BrF and IF

The vacuum ultraviolet photoelectron spectra of BrF (X¹Σ⁺) and IF (X¹ Σ⁺) have been recorded and interpreted with the aid of both MS — Xα — SCF calculations and ab initio calculations. For both BrF and IF the first band is split by spin—orbit coupling into two components corresponding to ionization to the X²Π$\text{3}\text{2}$ Phytochemistry and X²Π$\text{1}\text{2}$ ionic states. Estimates of re, ?we and De for these states have been made.     

PES studies of semiconductor - metal transitions in metal oxides

Semiconductor-Metal transitions in Ti₂O₃, VO₂, V₂O₃ and Ti₃O₅ have been investigated employing X-ray and UV Photoelectron spectroscopy. The transitions are accompanied by significant changes in the 3d band of the transition metals as well as some of the core levels.     

Interaction of carbon monoxide with transition metal surfaces

XPS studies of the interaction of carbon monoxide with surfaces of Fe, Co and Ni indicate that at 300 K, the disproportionation reaction is prominent up to exposures of 10³ L giving rise to high surface concentrations of carbon. At higher exposures and higher temperatures, dissociation of carbon monoxide accompanied by the formation of surface oxide layers becomes more prominent. In the case of copper, disproportionation is prominent up to 10⁴ L even at 500 K followed by dissociation at higher exposures. These results are also supported by Auger spectroscopic studies.     

XPES studies of oxides of second- and third-row transition metals including rare earths

X-ray photoelectron spectroscopy has been employed to investigate oxides of second- and third-row transition metals, including those of rare earths. Systematics in the spin—orbit splittings and binding energies of core levels of the metals are described. In most of the cases studied, the dependence of the spin—orbit splittings on the atomic number Z is given by the relation ΔE = a(Z - Z₀)⁴, where a is the quantum defect parameter and Z₀ is the effective screening. Core-level binding energies are found to increase with the oxidation state of the metal. Most of the core-level binding energies are related to the atomic number Z by the expression E = x(Z - Z₀)², giving rise to linear plots of ln E versus ln Z. Specific features of individual oxides, with respect to satellites, multiplet structure, configuration mixing, and other properties are also discussed. The spectra of PrO₂, Pr₆O₁₁, TbO₂ and Tb₄O₇ are reported for the first time.     

Satellite phenomena in the X-ray photoelectron spectra of lanthanide trihydroxides

Using the direct CI method perturbation corrections to the Koopmans ionization energies have been obtained up to order 10 for the molecules CN^? and H₂O. The results are compared with those from the fully converged CI and B_k-type calculations. The convergence of the perturbation series is found to be quite slow although substantial improvement is possible using a variation-perturbation method.     

Metal Auger intensity ratios as a probe for change-transfer effects in aluminum-covered transition metal surfaces

Marked changes in the LVV/LMV and LVV/LMM Auger intensity ratios of Co, Ni and Cu are observed on depositing Al on their surfaces. These changes, ascribed to charge-transfer or hybridization effects, are accompanied by changes in the intensity of the satellites next to the core levels of the transition metals.     

2D surface phonons in high-resolution electron-energy-loss spectra of metallic oxides

Surface phonon features in high-resolution electron-energy-loss (HREEL) spectra of the metallic tungsten bronze oxide Na_0.7WO₃ are much weaker than for insulating WO₃. Models based on the bulk dielectric function ?(ω) are unable to rationalise these spectra, but a simple two-layer model involving an unscreened surface dielectric layer is shown to account for both the intensities of the metallic phonons and their energies relative to those for WO₃. The sensitivity of HREELS to details of surface structure in metallic oxides is emphasised.     

Angle-resolved photoelectron spectra of ethylene as a function of photon energy using synchrotron radiation

As a test of the applicability of multiple-scattering theory to an unsaturated organic system, angle-resolved photoelectron spectra of the first four bands of ethylene have been measured from 1.5 eV above threshold to a photon energy of 28 eV. The results are compared to the multiple-scattering theory calculations of Grimm. The comparisons are excellent except for the 1 b_3u orbital below 14 eV, and the disagreement is attributed to the occurrence of autoionization. It is found that the π orbital has a much higher β value than the σ orbitals, but the β value for the π orbital varies more rapidly than that for the σ orbitals from threshold to ～0.5 Rydberg (～7 eV).     

He(I) and He(II) photoelectron spectra of some substituted ethylenes

The He(I) and He(II) photoelectron spectra of acrolein, acrylic acid, methyl acrylate, vinyl acetate, acrylamide and some of their methyl-substituted analogues are reported. Detailed assignments are proposed, mainly based on differences in intensity between the He(I) and He(II) spectra, on sum rule considerations and on the results of modified CNDO/S calculations.The assignment criteria are critically evaluated.     

He(I) and He(II) photoelectron spectra of iron tetracarbonyl-olefin complexes

The He(I) and He(II) photoelectron spectra of a series of iron tetracarbonyl—olefin complexes (olefin = acrolein, crotonaldehyde, methyl acrylate, acrylic acid, dimethyl maleate and some dihalogenated ethylenes) are reported. Assignments are proposed, based on differences in intensity between the He(I) and He(II) spectra, in comparison with related compounds and the results of extended CNDO calculations. The electronic structure of the coordinated olefins is discussed.     

Mössbauer studies of inorganic glasses through their glass transition temperatures

⁵⁷Fe Mössbauer studies of three inorganic glasses through their glass transition temperatures, T_g, show that the Lamb-Mössbauer factor (recoil-free fraction) decreases with temperature, particularly around T_g. An attempt is made to explain the results employing the cluster model which suggests that soft modes may be associated with the glass transition.     

A ΔSCF MO investigation of core-ionized states of some first-row transition metal ions

Non-empirical LCAO MO SCF computations have been carried out on a series of first-row transition metal ions in a variety of model lattice sites. The data allow a discussion of the shifts in binding energy and changes in relaxation energy as functions of the oxidation state and electronic environment. It is shown that the dominant contribution to the relaxation energy originates in the 3d valence-orbital component.     

Angular distribution of the photoelectron spectra for ethylene,propylene, butene and butadiene

The photoelectron spectra using the He I resonance line (21.22 eV) were measured for ethylene, propylene, 1-butene, cis-butene, trans-butene and 1,3-butadiene as a function of angle between the direction of the incoming photons and outgoing photoelectrons. From these data the angular parameter, β, is obtained for each photoelectron peak in each spectrum. The β value is a function of the energy of the photoelectron and the nature of the molecular orbital from which the photoelectron is ejected. A qualitative comparison is made between the experimentally derived β values and the molecular orbital assignments. In particular, it is noted that the photoelectron peak corresponding to the CC double bond π orbital yields a relatively high value of β. This has led in the case of butadiene to a confirmation that the first two photoelectron peaks both result from ionization in π orbitals.     

New method for photoelectron spectroscopy of solutions

A new method of rather general scope is reported for the determination of the photoionization (PI) spectra of solutions. Spectra thus obtained correspond to PI for ejection of quasi-free electrons into the liquid phase. The method is based upon photoelectron emission (PEE) into vacuum by the solution upon irradiation with adjustable photon energy. A new instrument is described which features irradiation (up to 10 eV) of a film of the solution on the rim of a rotating disk target (72 r.p.m.). Two types of data are obtained: PEE quantum yield per incident photon as a function of photon energy; energy distribution curve (EDC) of electrons emitted into vacuum at given photon energies. The PI cross-section is obtained as a function of photon energy by the previously developed method of EDC superposition. The method is applicable even when the contribution by the solvent to total PEE is dominant. Application is made to PI by 0.4 M indole in glycol for irradiation from 6.5 to 10 eV. Experimental results include: the effect of equilibrium vapor pressure (3.5 × 10^?3 ? 4.6 × 10^?2 torr) on EDC's; PEE spectral response of solvent and solution; EDC's from 6.5 to 10 eV. Interpretation covers these results and also includes: attenuation of the photon flux in the gas phase; PI in the gas phase; changes of temperature and solute concentration caused by evaporation. The PI spectrum of indole in glycol at ?7 °C exhibits a band for bound-continuum transitions (rising segment up to ≈ 7.0 eV) and a superimposed band (maximum at ≈ 7.6 eV) for PI via autoionization of excited bound states. Systematic development of the photoionization spectroscopy of solutions up to 10 eV is made possible by this approach. Application of the rotating disk methodology to higher photon energies (HeI, ESCA) may be of interest.     

Relative Cl 2p:P 2s photoionization intensities in transition metal complexes

X-ray photoelectron spectra of the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$}, P 2s region were obtained for nine transition metal complexes. The Cl:P atom ratios ranged from 1:3 to 3:2 and exhibited a linear relationship with the Cl 2p_{$\text{1}\text{2}$, $\text{3}\text{2}$} : P 2s intensities. Using AlKα radiation, the ratio of the Cl 2p: P 2s photoionization intensities was found to be 2.5: 1.0 with the McPherson ESCA-36 Photoelectron Spectrometer operated in its standard configuration.     

New depth-profiling method by angular-dependent x-ray photoelectron spectroscopy

A non-destructive method for depth profiling by X-ray photoelectron spectroscopy, based on the dependence of the analysed depth with the electron emission angle, is presented.The extraction of the concentration profile from angular distribution experiments is achieved, in the framework of a flat-layer model, by minimizing the difference between theoretical and experimental relative intensities. The applicability and limitations of the method are discussed on the basis of computer simulation results. In particular, constraints reflecting the physical properties of the system must be introduced in the numerical treatments. The depth probed is of the order of 3λ, λ being the value of the inelastic mean free path, and the depth resolution is of the order of λ/3. In tests of the method, the concentration depth profiles of the Ag-Al₂O₃ and the SiO₂-Si interfaces and of the surface region of a Cu-Ni alloy have been obtained.     

X-ray photoelectron spectroscopy of TiO2 and other titanate electrodes and various standard Titanium oxide materials: Surface compositional changes of the TiO2 electrode during photoelectrolysis

Surface compositional changes were observed for TiO₂ single crystal electrodes used for photoelectrolysis of water. Surface stoichiometries of several types of TiO₂, SrTiO₃ and BaTiO₃ electrodes were characterized by XPS and compared with a variety of titanium, titanium oxide and titanium hydride standard materials. Reduction of the electrode surface in a hydrogen atmosphere results in an oxygen deficient surface composition. Photoelectrolysis at current densities of $\text{10–15}\text{mA}\text{cm}{}^2$ for periods up to 8 h appears to return the electrode surface to a nearly stoichiometric oxygen-to-metal ratio. Reduction of the titanium oxide surfaces was also observed by exposure to an argon ion beam. Analysis of the electrode surface by a combination of XPS and ion-sputter profiling was still possible by simultaneous analysis of standard materials.     

Theory of spin-flip excitations across the ferromagnetic stoner gap in electron energy loss

We present calculations based on a simplified band model of the spin-flip cross section expected in electron energy loss in a ferromagnetic metal. It is shown how direct production of Stoner excitations can lead to observable features in both spin polarized and ordinary EELS spectra. A strong primary electron energy dependence is predicted for all these spin-flip features, in agreement with recent experiments.