HeI Spectra Research Articles

The electronic structure of heteroaromatic molecules; ab initio calculations and photoelectron spectra for the aza derivatives of benzo[c] furan, benzo [c] thiophen, N-methyl isoindole and related compounds

The HeI and II photoelectron spectra obtained for 2,1-benzisothiazole and 2,1,3-benzothiadiazole, and the HeI spectra for the corresponding O- and NMe-heterocycles have been satisfactorily interpreted, by means of a combination of variations between compounds and ab initio MO calculations; a comparison has been made with both the parent systems benzo[c]thiophen etc., and with the monocyclic compounds.

The valence electronic structure of SeO 2 studied by ups and its relation to that of other group VIB dioxides

HeI and HeII spectra of SeO 2 are presented and are analysed with reference to published work on the valence-shell structure of other group VIB dioxides. Orbital trends are discussed and the importance of processes involving two electrons in the valence-shell photoelectron spectra of all members of this group is noted. Where relevant the results of detailed studies of dioxides other than SeO 2 are presented to help clarify the analysis.

Valence Electron Spectra of Benzene and the Hexafluorides of Sulphur, Molybdenum, Tungsten and Uranium. An Application of Multichannel Detector Technique to UV-Valence Electron Spectroscopy

HeI induced valence electron spectra of benzene and the hexafluorides of sulphur, molybdenum, tungsten and uranium are presented together with a HeII spectrum of sulphur hexafluoride. Vibrational band structure has been resolved in the spectra of all molecules and the energies of these bands are reported. A description is also given of the multichannel detector system which has facilitated the recordings of these spectra.

A model for P CYG based on the HeI spectrum.

view Abstract Citations (11) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A model for P Cygni based on the He I spectrum. Oegerle, W. R. ; van Blerkom, D. Abstract Recent work on the interpretation of hydrogen emission lines from P Cygni has led to contradictory models of its atmosphere. In order to resolve the problem, we have constructed a model for He i emission in an accelerating envelope. The statistical equilibrium equations are solved at several points in the envelope using a 36 level neutral helium atom with continuum and the escape probability method to simplify the transfer of radiation. The resulting line profiles agree quite well with the observed lines for a mass loss rate of 2 x 10-6 M0 yr -`. The unusual behavior of helium lines, noted by Adams and Merrill, in which absorption components of lines in the same series have quite different displacements from line center, is a natural consequence of our model. The evidence of the radial velocity-excitation potential relation together with our line profile results point strongly to an accelerating flow in the region of P Cygni's envelope where the He I spectrum is formed. Subject headings: line profiles - stars: atmospheres - stars: circumstellar shells - stars: emission-line Publication: The Astrophysical Journal Pub Date: September 1976 DOI: 10.1086/154626 Bibcode: 1976ApJ...208..453O full text sources ADS | data products SIMBAD (1)

Oxidation of nickel studied by UV and X-ray photoelectron spectroscopy

The nature of argon-ion bombarded nickel surfaces (polycrystalline, and (111), (110) and (100) single crystals) and their subsequent interaction with oxygen at ordinary temperatures have been studied using X-ray and UV photoelectron spectroscopy, including angular variation measurements and the determination of work function changes, in combination in the same apparatus. Variations between the HeI spectra of the four clean substrates were taken to confirm the presence of substantial order within the depth sampled by UPS. The four surfaces exhibited similar but not identical behaviour during oxidation, resembling that reported by other workers from studies of both annealed single crystals and evaporated polycrystalline films. The initial process was deduced to be essentially dissociative chemisorption: no evidence supporting a previous suggestion of associative adsorption at low coverages was found. Oxygen commenced to penetrate below the surface of all samples before oxygen equivalent to a monolayer had been taken up (~10 L exposure) and further substantial uptake followed resulting in the formation of a stable film (~18 Å) of nickel oxide by ~100 L exposure. This oxide layer was not stoichiometric nickel(II) oxide: it was characterized by the presence of two distinct O 1s signals, the relative intensities of which depended on the crystallographic nature of the surface. It is tentatively suggested that the oxygen signal with the higher BE be associated with Ni III. Comparison of the X-ray and UV spectra suggests that the oxide film is very non-uniform in thickness, some Ni metal remaining very close to the surface.

Ultraviolet photoelectron spectra of thiazyl chloride

The He I, He II, and Ne I ultraviolet photoelectron spectra of thiazyl chloride, NSCl, are reported. The HeI spectrum exhibits five bands which, on the basis of correlation with related eighteen valence electron systems and CNDO/2 calculations, are assigned to seven ionic states. Relative intensity measurements on the He I and He II spectra suggest that the first three ionic states arise from electron ejection from orbitals which contain a proportionately larger share of CI 3p orbital character, whereas the next three ionic states correspond to orbitals containing more NS orbital character. The last ionic state is assigned to ionization from an orbital containing significant S 3s character.

Angular-resolved HeI photoelectron spectra for the (001) face of a copper single crystal

The anisotropy in the emission of photoelectrons from the (001) face of a cleaned copper crystal has been investigated. The electron distribution curves for electrons emitted from the surface, after excitation by normally incident HeI photons, are presented for varying analyser angles to the surface normals and projecting along the Gamma X and Gamma K directions of the (001) surface Brillouin zone. The experimental data have been interpreted, in part, in terms of direct interband transitions with the aid of existing APW band-structure calculations. A dependence of the HeI spectra on the photon incidence angle has been observed.

Electronic structure of the oxides of lead. Part 1.—A study using X-ray and ultraviolet photoelectron spectroscopy of the oxidation of polycrystalline lead

HeI and HeII spectra of clean polycrystalline lead are reported and discussed. The oxidation of this polycrystalline lead foil by both ground-state molecular and microwave-excited oxygen has been studied using UPS and XPS techniques in combination in the same apparatus. Work function changes were also measured. The initial process is deduced to be dissociative adsorption of oxygen leading to a lead-rich surface oxide, which then oxidises more slowly with continued exposure to form rhombic PbO : the production of PbO at the surface is shown to take much longer than was hitherto thought necessary.

Photoemission from gallium selenide using synchrotron radiation

The valence band structure of single-crystal GaSe has been studied by photoelectron emission using synchrotron radiation. Features in the energy distribution curves vary in amplitude with increasing photon energy in a manner consistent with direct transitions from three high-density valence band regions. The results are compared with HeI and X-ray photoemission spectra and discussed in terms of available band calculations.

Ultra-violet and X-ray photoelectron spectroscopy studies of oxygen chemisorption on copper, silver and gold

A photoelectron study (HeI, HeII and Mg Kα) of the oxidation at ordinary temperatures of polycrystalline copper, silver and gold, by both ground-state molecular and excited oxygen has established which oxidation states of these metals are formed during and after the dissociative chemisorption of oxygen. Up to about a monolayer coverage, copper is converted to the Cu(I) state and thereafter, as oxygen uptake proceeds, to the Cu(II) state. Silver also initially forms a + 1 oxidation state, but both the magnitude of the line widths of, and the significant absence of satellites associated with the core-level peaks suggest that a diamagnetic Ag(III) oxide rather than Ag(II) is formed upon further oxidation. Gold does not proceed beyond the Au(I) state. The densities of states (as reflected in the HeII spectra) of the three metals offer less guidance as to the conditions or ease of formation of the M(I) oxide overlayers, than the energy differences between the s-band edges and the vacuum level.

Electronic structure of sulphur compounds VI. Photoelectron spectra of some simple thiocarbonyl compounds

The photoelectron spectra of a number of simple thiones including thiofenchone, thiocarbonates and thioamides have been recorded, and the bands corresponding to ionization energies in the range 7.5–13 eV have been interpreted using vibrational fine structure, comparison of He-I and He-II spectra, and CNDO/S calculations. In all compounds the non-bonded orbital mostly localized on the sulphur atom has the lowest ionization potential. The position of the bonding π and σ orbitals show a marked sensitivity to the nature of the substituents on the thiocarbonyl sulphur atom.

Photoelectron studies of metal carbonyls. Part 4.1—Mono-substituted complexes of chromium and tungsten carbonyls

The photoelectron spectra of complexes of the general formula [M(CO)5L], where M = Cr or W, and L = amine, phosphine or isonitrile, have been examined using He I radiation and that of [Cr(CO)5 NMe3] using He II radiation. A clear splitting of the predominantly metal d-levels into e and b2 components is resolved in the case of the amine derivatives, and an asymmetric band envelope is found for the phosphine and isonitrile complexes. The assignment of these bands is facilitated by the presence of spin-orbit splitting of the e level in the tungsten complexes. The reasons for the e–b2 splitting are discussed with aid of ab initio SCF–MO calculations of [Cr(CO)5NH3] and [Cr(CO)5PH3] which do not suggest that a simple explanation in terms of the π-acceptor character of the substituent is valid. The M—L σ-bonding level is clearly separated from the d-orbital region, and exhibits anomalously high relative intensity in the HeI spectrum.

Transmission probabilities of high-frequency phonons through a solid-He-II interface

The transmission of monochromatic, high-frequency phonons from a solid into He-II by single-quantum processes is calculated. The roton minimum and especially pronounced the phonon maximum of the He-II spectrum show up as peaks in the transmission coefficient.

Photoelectron spectra of halides. Part III. Trifluorides and oxide trifluorides of nitrogen and phosphorus, and phosphorus oxide trichloride

High-resolution photoelectron spectra, obtained with HeI(584 A) and HeII(304 A) resonance radiation, are reported for NF3, PF3, NOF3, and POF3. A low-resolution HeI spectrum of POCl3 is also reported; vertical ionisation potentials (i.p.) and in many cases estimates of adiabatic i.p. also, are tabulated for all the compounds. The agreement of the experimental orbital assignments with ab initio calculations is excellent for PF3, POF3, PCl3, POCl3, good for NF3, but less good for NOF3. The correlations of the energy levels of PF3 with those of POF3, and of PCl3 with POCl3, follow a simple pattern of strong stabilisation of the lone pair of the donor molecule upon bonding to the O atom, with smaller stabilisations of the remaining orbitals. Correlations of the levels of POCl3 with those of SiCl4, and of POF3 with SiF4 are similarly satisfactory, but no simple pattern appears in the correlation of NOF3 with CF4 or with NF3.