Photoelectron spectra and SCF MO calculations for the dimers of cyclobutadiene

The He I photoelectron spectra of the syn and anti dimers of cyclobutadiene have been measured. Accurate MINDO/2 SCF MO calculations, in which the geometries of both dimers were optimized, have been used in interpreting the spectra. The experimental ionization energies derived from the spectra are in reasonable accord with those reported recently by Heilbronner and co-workers. However, the current interpretation of the photoelectron spectrum of the syn dimer differs significantly from that of the earlier one.     

Photoelectron spectra of bicyclic peroxides

The He(I) photoelectron spectra of nine bicyclic alkyl peroxide have been recorded. The first peaks are assigned by comparison with results of a MINDO/3 calculation. A correlation between the split of the first two ionization potentials and the OO torsional angle Θ is found.     

Photoelectron spectra and orbital assignments by sum rule consideration: Ethyl and n-propyl fluorides

The He I photoelectron (PE) spectra of C₂H₅F and n-C₃H₇F have been obtained. The PE spectra indicate that the first ionization potentials are about 0.4 eV higher than those of the parent alkanes owing to the inductive effect of fluorine. All the PE bands obtained here have been interpreted in terms of appropriate p-type localized MO's using the sum rule described previously by the authors. Orbital energy diagrams involving the inductive effect of fluorine are illustrated. The semi-empirical CNDO/2 and MINDO/2 methods were also employed to help confirm the present orbital assignments.     

Photoelektronenspektren und konformationsverhalten von hydroxylamin und methylhydroxylaminen

Gas-phase He(I) photoelectron spectra of hydroxylamine (1) and the methyl hydroxylamines (2–6) have been measured. From 1 a He(II) spectrum has also been obtained. To study the interactions of the n(N) and n(O) orbitals, MINDO/2 calculations have been performed for various conformations of 1–6. The findings are consistent with trans- forms being the most stable conformations of 1–6, but additional cis- conformers cannot be excluded.     

Semiempirical molecular orbital techniques applied to silicon dioxide: MINDO/3

We present a discussion of MINDO/3, a semiempirical molecular orbital program, which we have applied to clusters of atoms used to represent silicon dioxide. We have obtained MINDO/3 parameters for the Si-O interaction and have calculated a variety of observables for both molecules and solid-state clusters, for both open- and closed-shell systems. With some exceptions, we find very good agreement with other calculations and with experiment. In particular, our results for both E′₁ and E′₄ defects support existing models which feature asymmetric atomic relaxations.     

Angle-resolved photoelectron spectroscopy of benzene and hexafluorobenzene as a function of photon energy

Angle-resolved photoelectron spectra of benzene have been recorded using synchrotron radiation as the photon source. From these results the angular dis the first three orbitals; 1e_1g(π), 3e_2g (σ) and 1a_2u(π). Calculations of β employing the MS Xα method have also b and theory for the first two orbitals is excellent. Poor agreement in the core of the third orbital is believed to be due to overlap of the second and has been verified by data obtained for perfluorobenzene. The universality of the energy dependence of β for π orbitals, noted previously for unsatu aromatic systems. The importance of the results for benzene for the future application of angle-resolved photoelectron spectroscopy to complex molecule     

Photoelektronenspektren organischer verbindungen: III. Photoelektronenspektren acetylensubstituierter kleiner ringe

The high resolution He I photoelectron spectra of vinylacetylene, cyclopropylacetylene, cyclobutylacetylene and cyclohexylacetylene are reported and ionization potentials in the low-binding region are assigned by correlating the spectra with spectra of reference compounds, by using the information supplied by vibrational analysis and by comparing the assignment with the results of MINDO/2 calculations. The resonance integrals β_RS between the π type orbitals of the acetylene moiety (R) and the π and Walsh type orbitals of the substituents (S) are determined by means of a LCMO model, parametrized with spectra of known assignment. The interaction terms H_Rs of cyclopropylacetylene, which are 1.3 eV in the bisected conformation and 0.7 eV in the perpendicular conformation, can be considered as experimental verification of the correlation diagram for vinylcyclopropane given by Hoffmann et al. and provide an explanation of the stability of the gauche conformation of vinylcyclopropane. In the case of cyclobutylacetylene, only estimated values of the interaction term H_RS can be obtained from the spectrum.     

Sum rule consideration on valence orbital ionization energies in methyl amines

A sum rule treatment using Hall's equivalent orbitals has been applied to the valence orbital ionization energies of mono-, di- and trimethylamine up to about 40 eV assuming Koopman's theorem. Excellent agreement is obtained between theory and experiment in partial and total energy sums. A similar treatment using p-type localized orbitals previously proposed by the authors is also applied to ionization energies below about 18 eV for the methyl amines. In these sum rule treatments we use both the vertical ionization energies obtained from He (I) photoelectron spectra measured here and the higher ionization energies deduced from the He (II) photoelectron spectra published by Potts et al. The complete sets of valence orbital ionization energies of the methyl amines have thus been identified by sum rule considerations in photoelectron spectroscopy. We show that the character of the corresponding MO's may be inferred from the sum rule. The orbital orderings and characters of the methyl amines have also been studied by CNDO/2 and MINDO/2 methods.     

Correlation effects in the photoelectron spectra of 3d metals

An approximate method is presented for calculation of the orbital relaxation in photoelectron spectra for systems with a continuous distribution of electron states. The results for Fe, Ni and Cu 3d states explain the discrepancy between experimental data and band structure calculations. The nature of the satellite in photoelectron spectra of Ni is discussed.     

Influence of elastic-scattering processes on an X-ray photoelectron spectroscopy signal: Effect of the underlying surface

The boundary-value problem for the transfer equation with internal sources and without them is solved using the invariant embedding method. The influence of processes of photoelectron elastic scattering on the energy spectra of photoelectron emission is analyzed. The focus of attention is on the analysis of variations in the intensity and the spectral composition of the ascending flow of the photoelectron emission of a layer when underlying layers with different compositions appear. The physical fundamentals of the influence of elastic scattering on the formation of X-ray photoelectron spectra are demonstrated. The peak intensities for homogeneous Au 4s _1/2 and Si 2s _1/2 targets are calculated with and without the inclusion of reflection processes. The error appearing as a result of neglecting elastic scattering processes, which transform the descending motion into ascending type, is determined.     

Gas phase and solid state X-ray photoelectron spectra of the substituted acetylenes (SF5)n C2 (CF3)2−n (n = 0, 1, 2): A comparison of the pentafluorosulfur and trifluoromethyl groups

The core level X-ray photoelectron spectra (XPS) of CF₃CCCF₃, CF₃CCSF₅ and SF₅CCSF₅ have been measured in the solid state. Gas phase spectra of CF₃CCCF₃ and CF₃CCSF₅ have also been obtained. The XPS data, interpreted with the point charge potential model and semiempirical MNDO (minimum neglect of differential overlap) molecular orbital calculations, indicate that the electron withdrawing effect of the ?CF₃ group is greater than that of the ?SF₅ group. Results further suggest that sulfur 3d orbitals do not play a detectable role in the bonding or charge distribution in these molecules. Carbon 1s linewidths of ?CF₃ carbon atoms are found to be much narrower than those arising from the acetylenic carbon atoms. The narrower lines correlate with the much higher binding energy of the ?CF₃ carbon atoms. Large shifts (nearly 1 eV) in heteroatom core level binding energy differences (for example, F 1s — C 1s) between the gas phase and solid state data are observed. These shifts are attributed to solid state effects (Madelung potential, intermolecular bonding interactions, and/or extramolecular relaxation contributions). From these comparisons it is clear that solid state effects are not uniform in their influence on the photoionized sites in these molecules.     

烯3(C_(10)H_(16))Raman光谱的量化计算研究

烯３（Ｃ１０Ｈ１６）Ｒａｍａｎ光谱的量化计算研究赵永年（吉林大学超硬材料国家重点实验室吉林大学超分子结构与光谱开放实验室）ＡＱｕａｎｔｕｍＣｈｅｍｉｓｔｒｙＣａｌｃｕｌａｔｉｏｎＳｔｕｄｙｏｆｔｈｅＲａｍａｎＳｐｅｃｔｒｕｍｏｆＣａｒ┐３┐ｅｎｅ（Ｃ...     

Theoretical and experimental investigation of the influence of external effects on the electronic structure of Ce-based heavy-fermion systems

The electronic structure of Ce systems with different degrees of hybridization of f electrons with outer-shell electrons and the effect of pressure on the change in the electronic structure has been investigated. A correlation between the parameters of X-ray photoelectron spectra and the magnitude of the heavy-fermion state is established. The total and partial densities of states of atoms were calculated using the TB LMTO ASA method. X-ray photoelectron study of the effect of an X-ray induced vacancy in the inner levels on the shape of the Ce3d spectra for Ce-based systems with different degrees of covalence has been performed. It is shown that there is a relationship between the magnitude of the heavy-fermion state and the intensity of the shakedown satellites in X-ray photoelectron spectra and that the magnitude of the heavy-fermion state decreases under pressure.     

A Mössbauer effect study of the bonding in several organoiron carbonyl clusters

After a brief review of the applications of the Mössbauer effect to cyclopentadienyl containing compounds, the chemistry and spectral properties of the various iron carbonyl complexes are described. The electronic properties of a series of trinuclear and tetranuclear organoiron clusters have been investigated through Fenske-Hall self-consistent field molecular orbital calculations, and the results are compared with the Mössbauer effect isomer shifts. A linear correlation is found between the Slater effective nuclear charge, as calculated from the Fenske-Hall partial orbital occupancy factors, and the isomer shift. In these compounds the 4s orbital populations are rather constant. However, thecis andtrans isomers of [CpFe(CO)₂]₂ have a significantly lower 4s orbital populations. In this case, the reduced 4s population must be accounted for by adding it to the effective nuclear charge to obtain a good correlation with the isomer shift.     

Subshell photoionization cross-sections,electron mean free paths and quantitative X-ray photoelectron spectroscopy

Subshell photoionization cross-sections (SPC) for elements of atomic number in the range 3?, z ? 82 have been determined from measurement of relative photoelectron intensities at a photon energy of 1486.6 eV (Al Kα). A correction procedure has been developed which permits such determinations even when sample surfaces are not atomically clean. The results obtained suggest that Scofield's SPC calculations [2] are reasonably reliable for 1s, 2p and 3d subshells but that the present, experimentally derived data are to be preferred for quantitative use. As a result of this work, a rapid method of quantitative surface-constituent analysis, accurate to ± 20%, has also been developed, which is expected to be of value particularly in industrial situations. A semi-empirical method of extracting electron mean free paths from measurements of relative photoelectron intensities is also illustrated.     

MINDO/3 calculation of the electronic structure of silicon nitride

The electronic structure of silicon nitride has been calculated by the semiempirical quantumchemical method MINDO/3 in the cluster approximation. The effect of cluster size and of boundary conditions on the partial density of one-electron states is analyzed. The results of the calculation are compared with experimental data on amorphous silicon nitride. The origin of a peak in the upper part of the valence band, which is seen in the SiL2,3 spectrum but not reproduced in the calculations is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 1342–1347 (August 1997)     

Study of the x-ray photoelectron spectrum of tungsten—tungsten oxide as a function of thickness of the surface oxide layer

The photoelectron spectrum of tungsten metal using Al K_α X-rays has been studied as a function of a tungsten oxide layer on the surface. The photoelectron lines arising from the 4f shell of tungsten metal are clearly separated in energy from those coming from WO₃. The ratio of the intensities of these two sets of lines were measured for a series of metal samples which were anodized to a determined level of tungsten oxide. The data were shown to be consistent with a uniform deposition of oxide film. The escape depth, or thickness from which half the photoelectron intensity is derived, was found for a 1450 eV photoelectron to be 8.9 Å and 18.3 Å for W and WO₃, respectively.     

Isomerization mechanisms from cis to trans form in polyacetylene

Mechanisms of cis-trans irreversible isomerizations occurring in both thermal treatment and doping of polyacetylene are presented and examined by means of MINDO/3 molecular orbital calculations on some finite polyenes. It is predicted that the thermal isomerization proceeds along the internal rotation of (-CH=CH-) unit around two carbon-carbon double bonds via the transition state having a biradical nature. Meanwhile, the isomerization by doping is rationalized by the mechanism that the cis segment between two doping sites is converted into the trans-cisoid form which rotates easily around two single bonds to yield some trans forms in (CH)_x chain.     

UV Subshell photoionisation cross-section of atomic Zn,Cd, and Hg: Experiment and theory

Partial photoionisation cross-sections have been measured at photon wavelengths of 584, 304, 256 and 243 Å for the valence d and s shells of zinc, cadmium and mercury atoms. These cross-sections have also been calculated using the GIPM, a simple one-electron method which obtains the final-state potential by an inversion of the Schrödinger equation for the initial orbital of the photoelectron in the Hartree-Fock wave function. Comparison shows good qualitative agreement between theory and experiment. The quantitative agreement is typically within a factor of 2. Angular asymmetry parameters have also been calculated and the branching ratio for the splitting of the d-subshell cross-section into ²D_{$\text{5}\text{2}$} and ²D_{$\text{3}\text{2}$} contributions has been measured.     

The nature of a selective peak in the BK-absorption edge spectrum and the electronic energy band structure of the crystal 3C BN0.99

A new interpretation of the nature of the resonance in the quantum-yield K spectra of boron in the crystal 3C BN is proposed. This interpretation is based on calculation of the electronic energy band structure of the nonstoichiometric boron nitride 3C BN_0.99, which is carried out by the local coherent potential method in the multiple-scattering approximation. The tops of the valence band and of the XANES range of nonstoichiometric and perfect crystals of boron nitride are compared with the x-ray photoelectron spectrum of 3C BN and the BK-absorption edge spectrum. The electronic states near the BK-absorption edge are modeled and discussed for the relaxed and metastable states caused by the formation of vacancies in the nitrogen sublattice.