The electronic structure of carbon suboxide from ESCA and AB initio calculations

The ESCA spectrum of C₃O₂ excited by Mg K_α radiation, 1253.6 eV, has been obtained for both gaseous and solid samples. The chemical shifts of the C1s and O1s levels have been used to calculate the gross atomic charges. The valence region of the spectrum has been recorded and the ordering of the orbitals has been decided on the basis of an ab initio calculation and the intensities of the observed peaks. An unusually intense shake-up spectrum has also been observed and is discussed. The relative spacing of the valence peaks has been found to be different for the solid and gas.     

Shake-up peak positions and intensities by many-body theory methods

The valence shell X-ray photoelectron spectrum of N₂ is calculated using the equations-of-motion—Green's function method. The inclusion of shake-up basis operator configurations in the primary operator space along with the simple ionization operator configurations allows for the calculation of shake-up peak positions on an equal footing with the simple ionization energies. The important shake-up basis operator configurations are identified using configuration selection techniques similar to those which have been successfully employed in large scale configuration interaction problems, thus minimizing the size of the matrices to be diagonalized. The relative peak intensities are calculated within the plane wave approximation. The intensity equations are analyzed indicating that the relative peak intensities are more sensitive to ground state correlation effects than the peak positions. Modifications of the theory to improve the calculations of shake-up energies are discussed.     

A study of shake-up satellites in Co 2p photoelectron spectra of trans-[Co(NH3)4Cl2]Cl and cis-[Co(NH3)4Cl2]Cl isomers

Mg Kα X-ray photoelectron (ESCA) spectra of the Co 2p levels have been obtained in trans- and cis-[Co(NH₃)₄Cl₂]Cl isomers. It is observed that these compounds slowly decompose under X-ray irradiation. A procedure is employed to record real spectra for both the trans and cis isomers without any significant complication by the decomposition products. Three satellites are observed in both spectra at binding energies ≈ 4.8 eV, ≈ 9.3 eV, and ≈ 16.5 eV greater than that of the Co 2p_{$\text{3}\text{2}$} peak. These isomers are distinguished from one another by the sizable difference in the relative intensity of the first satellite to the main peak. The first two satellites are assigned to ligand to Co 3d shake-up transitions by use of symmetry arguments based on molecular orbital theory, while the origin of the third satellite is less certain. The implication of the results is discussed.     

A study of the 1s core region of atomic magnesium by X-ray photoelectron spectroscopy

The 1s core region of atomic magnesium has been measured by X-ray photoelectron spectroscopy using AlKα (1486.6 eV) radiation in order to determine the energy and intensity of the main satellite corresponding to 3_s → 4_s excitation accompanying core ionization. It was found to lie at 11.56 eV higher bonding energy than the main 1s?1 peak, with a relative intensity of 17%. The accent ab initio Cl calculation of Kosugi and Kuroda gives a separation which is in good agreement with experiment but somewhat overestimates the relative intensity.     

High resolution electron momentum spectroscopy of the valence orbitals of water

The development of a third-generation electron momentum spectrometer with significantly improved energy and momentum resolutions at Tsinghua University (ΔE = 0.45–0.68 eV, Δθ = ±0.53° and Δ? = ±0.84°) has enabled a reinvestigation of the valence orbital electron momentum distributions of H₂O with improved statistical accuracy. The measurements have been conducted at impact energies of 1200 eV and 2400 eV in order to check the validity of the plane wave impulse approximation. The obtained ionization spectra and electron momentum distributions have been compared with the results of computations carried out with Hartree Fock [HF] theory, density functional theory in conjunction with the standard B3LYP functional, one-particle Green’s function [1p-GF] theory along with the third-order algebraic diagrammatic construction scheme [ADC(3)], symmetry adapted cluster configuration interaction [SAC-CI] theory, and a variety of multi-reference [MR-SDCI, MR-RSPT2, MR-RSPT3] theories. The influence of the basis set on the computed momentum distributions has been investigated further, using a variety of basis sets ranging from 6-31G to the almost complete d-aug-cc-pV6Z basis set. A main issue in the present work pertains to a shake-up band of very weak intensity at 27.1 eV, of which the related momentum distribution was analyzed for the first time. The experimental evidences and the most thorough theoretical calculations demonstrate that this band borrows its ionization intensity from the 2a₁ orbital.     

X-ray photoelectron spectra of metal complexes of substituted 2,4-pentanediones

The X-ray photoelectron spectra of 14 complexes of Al³⁺, Cr ³⁺, Fe³⁺, Co³⁺ and Cu²⁺ with 3-X-2,4-pentanedione (X = H, Cl, Br) were determined to analyse the nature of metal-ligand bonding in these complexes. The trend in the position of np photoelectron lines of X-group with a change of metal ion was decided by the relative contribution of metal-toligand and ligand-to-metal charge transfer. The analysis of the satellites in the M(2p_3/2) and M(2p_1/2) spectra suggested that the metal-ligand bond in the chromium(III) complex had higher covalent character than that in the iron(III) complex. The satellite separations in the O(1s) spectra of M(3-Xptdn)₃ were in the range 4.0-4.8 eV: these satellites were assigned to a shake-up transition of Lπ → Lπ^* character. The O(1s) spectra of Fe(3-Xptdn)₃ and A1(3-Xptdn)₃ displayed an additional strong peak to higher energy than that of the main peak (δE = 2.1–3.1 eV) when the samples of complexes were bombarded with argon ions for a longer time.     

Ab initio CI study and vibronic analysis of the photoelectron spectra of formaldoxime

The photoelectron spectrum of formaldoximie, CH₂NOH, has been re-investigated with higher resolution and interpreted by, means of ab initio SCF Cl calculations. Calculations have confirmed that the states increase in energy as π₁ < n₁ < π₂ < n₂ and have shown the existence of a shake-up peak at ≈15 eV. The calculation of Franck-Condon factors allowed the interpretation of the observed vibrational structure.     

TDS and XPS study of oxygen diffusion into subsurface layers of Pd(110)

Summary The interaction of O₂with Pd(110) has been studied by TDS and XPS at T = 400 K and at pressures P_{O2 from 2.6x10}^-6to 10 Pa. At low exposures in O₂(e￡1-5 L), an adsorption layer withqof ca.0.5 and with the O1s peak at BE = 529.3 eV has been found to form on the surface. Whenegrows from 5 to 10⁸L, the position and intensity of the oxygen O1s peak remain practically constant. At the same time, as much as 5 mL of oxygen is absorbed according to the TDS data. The results obtained by TDS and XPS indicate that oxygen penetrates deep into the subsurface layers of palladium (315-20 ?) and is distributed in its bulk in a low concentration.     

An ESCA study of the photo-oxidation of the surface of polystyrene film

The surface photo-oxidation of polystyrene film is examined using ESCA. The initial stage involves the formation, primarily, of CO groups on the surface. Further reaction produces carbonyl, carboxyl and carbonate groups, accompanied by the disappearance of the C_1s shake-up satellite peaks, indicating the photo-oxidation of the phenyl groups. The relative concentrations of these groups at the surface are followed as a function of oxidation time. The $\text{C}\text{O}$ peak intensity ratio indicates a limiting C:O stoichiometry in the surface of ～ 1·7:1, very different from the bulk of the polymer. Carboxyl groups predominate in this highly oxidised surface.     

XPS,UPS, and STM studies of nanostructured CuO films

A Cu₁O_1.7 oxide film containing a large amout of superstoichiometric oxygen was obtained by low-temperature oxidation of metallic copper in the oxygen plasma. An STM study of the film structure showed that ～10 nm planar copper oxide nanocrystallites with particles packed parallel to the starting metal surface. In an XPS study, the spectral characteristics of the Cu2p and O1s lines indicated that particles with a CuO lattice formed (E _bnd(Cu2p _3/2) = 933.3 eV and a shake-up satellite, E _bnd(O1s) = 529.3 eV). The additional superstoichiometric oxygen is localized at the sites of contact of nanoparticles in the interunit space and is characterized by a state with the binding energy E _bnd(O1s) = 531.2 eV. Due to the formation of a nanostructure in the films during low-temperature plasma oxidation, the resulting copper oxide has a much lower thermal stability than crystalline oxide CuO.     

Theoretical studies of excited states of H3O and of core-excited NH3: Comparisons with equivalent core analysis of NH3 core-excitation spectra and implications for the radiation chemistry of aqueous systems

The H₃O radical has been studied within the ab initio LCAO SCF MO model. A flexible basis set including diffuse basis functions at both O and H has been used in order to represent the excited states adequately. Calculated excitation energies are 1.87, 2.87–3.16, and 3.36–3.47 eV; the calculated ionization energy is 4.75 eV. These represent well the experimental values (good to ±0.3 eV) of 1.6, 2.9, and 3.5 eV for excitation, and 5.0 eV for ionization, deduced by equivalent core analysis of high energy electron impact energy loss studies of NH₃. Similar explicit calculations on the N-1s core-excited states of NH₃ have also been made to examine directly the equivalent core concept. “Excited states” (relative to the lowest bound core-excited state) at 1.72, 2.85–3.09, and 3.32 eV, and the “ionization energy” of 4.68 eV, agree well with experiment and support the equivalent core concept. The possible significance of these H₃O results in the radiation chemistry of aqueous media is discussed in view of the fact that the maximum in the absorption spectrum of the hydrated electron lies near that of H₃O.     

Approaching compositional limits of perovskite – type oxides and oxynitrides by synthesis of Mg0.25Ca0.65Y0.1Ti(O,N)3, Ca1–xYxZr(O,N)3 (0.1 ≤ x ≤ 0.4), and Sr1–xLaxZr(O,N)3 (0.1 ≤ x ≤ 0.4)

Partial substitution of cations and anions in perovskite-type materials is a powerful way to tune the desired properties. The systematic variation of the cations size, the partial exchange of O²⁻ for N³⁻ and their effect on the size of the optical band gap and the thermal stability was investigated here. The anionic substitution resulted in the formation of the orthorhombic perovskite-type oxynitrides Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃, Ca_1-xY_xZr(O,N)₃, and Sr_1–xLa_xZr(O,N)₃. A two-step synthesis protocol was applied: i) (nano-crystalline) oxide precursors were synthesized by a Pechini method followed by ii) ammonolysis in flowing NH₃ at T = 773 K (Ti) and T = 1273 K (Zr), respectively. High-temperature synthesis of such oxide precursors by solid–state reaction generally resulted in phase separation of the different A-site cations. Changes of the crystal structures were investigated by Rietveld refinements of the powder XRD data, thermal stability by DSC/TG measurements in oxygen atmosphere, oxygen and nitrogen contents by O/N analysis using hot gas extraction technique, and optical band gaps by photoluminescence spectroscopy. By moving from Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃ via Ca_1–xY_xZr(O,N)₃ to Sr_1–xLa_xZr(O,N)₃, the degree of tilting of the octahedral network is reduced, as observed by an increase in the B–X–B angles caused by the simultaneously increasing effective ionic radius of the A-site cation(s). In general, increasing substitution levels on the A-site (Y³⁺ and La³⁺) are accompanied by an enhanced replacement of O²⁻ by N³⁻. In all three systems, this anionic substitution resulted in a reduction of the optical band gap by approximately 1 eV (Ti) and up to 2.1 eV (Zr) compared to the respective oxides. For Mg_0.25Ca_0.65Y_0.1Ti(O,N)₃ an optical band gap of 2.2 eV was observed, appropriate for a solar water splitting photocatalyst. The Zr-based oxynitrides required a by a factor of 2 higher nitrogen contents to significantly reduce the optical band gap and the measured values of 2.9 eV–3.2 eV are larger compared to the Ti-based oxynitride. Bulk thermal stability was revealed up to T = 881 K. In general, the thermal stability decreased with increasing substitution levels due to an increasing deviation from the ideal anionic composition as demonstrated by O/N analysis.     

A study of valence ionization of ammonia with synchrotron radiation

Angular distributions of photoelectrons from the three valence levels of molecular ammonia, 2a₁ with a binding energy (BE) of 27.7 eV, 1e (BE = 16.3 eV) and 3a₁ (BE = 10.9 eV) have been measured in the 30–130 eV photon energy range. Comparison is made in the case of the 3a₁ molecular orbital with the calculated atomic N 2p asymmetry parameters. Photoionization branching ratios have also been obtained in this photon energy range and good agreement has been found with previous quasiphotoionization measurements and with the one-center-expansion calculations of Cacelli et al. The satellite structure in the inner valence (2a₁) region has been investigated at 60 eV and compared with a number of energy and intensity calculations.     

Application of anomalous oxygen Kα 532 eV peak for the determination of metal oxide thickness

Oxygen Kα spectra emitted from oxides formed on several metals were analysed with a potassium acid phthalate (KAP) crystal, which showed a strong anomalous peak due to the reflectivity spike of KAP at the particular energy region ～532 eV. The relative intensity of the 532 eV peak to the main peak decreased rapidly with the increase of the oxide thickness, while absolute intensities of both peaks increased. The relative intensity also changed depending upon an incident energy of electrons (E₀) to excite X-rays: for thick oxide it decreased relative to E₀, and for thin oxide it had a minimum value at E₀ ～5 ke V. These experimental features were well explained theoretically by taking into account a contribution both of characteristic and continuous X-rays to the 532 eV peak. As an application of this experiment, we propose a convenient, nondestructive determination of the oxide thickness.     

On the calculation of the satellite peaks observed in the high energy photoelectron spectra of small molecules

The shake-up peaks which are observed to high binding energy of the main photoionization peak in the high energy photoeletron spectra of CO (carbon and oxygen core holes), H₂O and NH₃ have been interpreted by an extension of the singly excited configuration interaction method used previously in the study of the low-lying excited states of these molecules. The results obtained provide a good interpretation of the experimental spectra of these molecules in terms of many shake-up states. It is concluded that relaxed orbitals and an extensive basis set, including diffuse functions, should be used in the calculations in order to obtain good results.     

Chemical effects of satellites on X-ray emission spectra-III: A theory of the origin of chemical effects for small covalency limits and its application to Cl Kα, spectra

A theory is presented to predict the satellite intensity of X-ray fluorescence spectra (XRF) for ionic compounds. The Asada-Sugano theory, which predicts the intensity of shake-up satellites of transition-metal compounds, has been applied to the calculation of shake-off satellite intensity of X-ray emission spectra. Covalency of outer shell is increased due to the creation of an inner-shell hole when the resonance condition holds. The spectator hole, which has been produced by shake-off is delocalized through the temporal molecular orbital formed by a resonance of atomic orbitals, thus the satellite intensity becomes weak. The probability of resonant electron transfer through the temporal molecular orbitals has been theoretically formulated by a two-configuration model. Satellite intensities of Cl K_α″ for LiCl, NaCl, KC1, RbCl and CsCl have been numerically calculated with the result that the satellite intensities of RbCl and CsCl have been found to be significantly weaker than those of LiCl, NaCl and KCl. The agreement between theory and experiment is good. This theory is found to be efficient for localized electron systems, which implies a potential for use with PIXE satellites emitted from localized deep-core levels.     

Finite-field many-body perturbation theory. VI. Multipole polarizabilities of beryllium. A comparative study

A high-resolution ESCA N1s spectrum from free p-aminobenzonitrile molecules is presented. The spectrum is very different from the corresponding spectrum from a solid sample. It shows one uncommonly intense shape-up line from the N1s ionization in the nitrile group, while ionization in the NH₂ group does not give rise to any such anomalous shake-up features. The spectrum is theoretically analyzed by means of a large-scale ab initio calculation by the CAS SCF method, in which a full π-orbital active space was employed for the ground and N1s ionic states. The calculations strongly underline the role of multiple excitations in the charge transfer following N1s(CN) ionization, as well as the importance of separate self-consistent treatment of all states involved. In particular, it is shown that an unsuitable choice of orbitals can lead to an apparent “shake-down”.     

Theoretical study of shake-up in the core photoelectron spectra of the alkali atoms

Relativistic and non-relativistic Hartree-Fock calculations have been performed for the shake-up lines relative to core ionization of the alkali atoms. Good general agreement with the experimental data is achieved both for the energy and the intensity. Relativistic effects are found to be small, amounting TO = 0.2 eV in Cs. As concerns the shake-up energies, a correlation effect is detected, the magnitude of which increases along the series.     

Ab initio configuration interaction calculations of the NIs (NO2) core-hole states of p-nitroaniline

The NIs (NO₂) core-hole states of p-nitroaniline are calculated by a Cl procedure that takes account of both orbital relaxation and correlation effects. A satellite peak arising from the excitation 4b₁(Π) → 5b₁(Π) is calculated to occur 26 eV from the main ionization peak, with a relative intensity of 66%. These results are compared with gas-phase photoelectron spectra.     

Core ionization of nitrosobenzene-dimer compounds: phenazon-di-N-oxide

The C 1s, N 1s and O 1s XPS spectra of soli d phenazon-di-N-oxide (PADNO) are presented in order to further elucidate the effects of intermolecular interactions in molecular solids on the dynamics of the core-ionization process. PADNO can be considered a model compound for an intramolecular cis nitrosobenzene dimer. The observed strong N 1s and O 1s shake-up intensity attenuations in going from the nitrosobenzene monomer to PADNO are discussed in detail based on the results of CNDO/S CI equivalent core calculations. The theoretical core-hole spectral functions are in excellent agreement with experiment. It is shown that the calculated shake-up intensities are strongly on electron correlation.