He(I) and He(II) photoelectron spectra of glycine and related molecules

Photoelectron spectra obtained by He(I) and He(II) excitation of glycine, sarcosine and glycine methyl ester are presented. The p-type bands in the He(I) spectrum of glycine are interpreted in terms of localized molecular orbitals; the C 2s bands are identified in the He(II) spectrum. He(I) spectra of some N-acetylamino acids and of a variety of α-and ω-substituted amino acids are also reported.     

The angular-distribution He(I)/Ne(I) photoelectron spectra of cyclopropane

The angular-distribution photoelectron spectrum of cyclopropane, studied with both He(I) and Ne(I) radiations, indicates negligible change in the asymm     

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.     

Photoionization cross sections: Interpretation of band intensities in He I and He II photoelectron spectra

Relative photoionization cross sections of molecules consisting of atoms from the first three rows of the Periodic Table are computed by a theoretical method developed previously which involves the plane-wave approximation for the photoelectron and the use of semiempirical LCAO-SCF-MO's of the CNDO- or MINDO- type for the initial orbital. The calculated values are compared with experimental photoelectron band intensities obtained by integrating the band areas in He I and He II photoelectron spectra. The observed relative intensity changes of bands in the spectrum in going from He I to He II excitation are attributed to variations in the one- and/or two-centre contributions to the cross sections from the electron density at the atoms and in the bonds, respectively. The analysis of the relative intensities of bands in the He I and He II spectra thus leads to conclusions about the electron density distribution in the initial orbital and about the assignment of the bands.In a qualitative sense, the experimental He I/He II intensity changes are usually correctly predicted by our theoretical method, but there are often considerable quantitative discrepancies between the measured and calculated values which probably arise from the inherent simplifications of our approach.     

He(II) photoelectron spectra of esters

Intensities of X-ray photoelectron transitions from the As 3d level are theoretically analysed taking into account many-electron interactions. The latter interactions profoundly affect the relative intensities of the transitions as well as binding energies. Implications for the surface structure of GaAs are then discussed and in particular we show that As atoms having the same chemical environment are spread over distances into the surface comparable to the interatomic spacing. This supports a recently proposed layer model for the untreated surface of GaAs.     

He(I) and He(II) photoelectron spectra of some organo-mercury compounds with carbon π-systems

The UV photoelectron spectra of a series of aromatic mercury derivatives {(C₆H₅)₂ Hg, (pCH₃C₆H₄)₂Hg, C₆H₅HgCl, pCH₃C₆H₄HgCl} and of a series of alkynyl mercury derivatives {(CH₃C)₂Hg, ((CCH₃)₃CCC)₂Hg, (ClCC)₂Hg} are reported and discussed. Particular attention is devoted to possible interactions between mercury orbitals and π systems of the ligands. In this respect differences are observed between the two series: in the alkynyl derivatives ligand-field effects are evident on the 5d mercury orbitals, whilst they are not observable in the aromatic compounds.     

The He(I) and He(II) photoelectron spectra of bis (2,4,6-tri-t-butylphenyl)-diphosphene

Photoelectron spectra of the title compound have been obtained using various ionising radiations. The bands up to ～10 eV have been assigned with the aid of molecular-orbital calculations.     

Fine structure in the He(I)/He(II) photoelectron spectra of the metal valence (d) shells of the group IIB dihalides

The He(I) and He(II) photoelectron spectra of the group IIB dihalides (except the difluorides) are reported. Emphasis is laid on the metal valence d-shell ionizations. These are discussed in terms of He(I)/He(II) relative intensity changes a ligand-field model. It appears that the observed d-shell structure is the result of a balance between simple field-effects and covalency.     

Theoretical interpretation of photoelectron spectra for transition metal compounds. The He(I) and He(II) spectra of MF2 molecules (M = Co,Ni and Cu)

Calculated vertical ionization energies (VIEs) and relative intensities (RIs) have been used in interpreting He(I) and He(II) photoelectron spectra of MF₂ molecules, M being Co, Ni and Cu. VIEs have been obtained by the Green's function technique applying the semiempirical CNDO-UHF method. Within the framework of the Gelius-Siegbahn model, but utilizing the theoretical atomic cross-sections, the molecular photoionization cross-sections (and the corresponding relative intensities of spectral bands) have been calculated for He(I) and He(II) spectra of MF₂ molecules. A comparison of the theoretical and experimental VIEs and RIs shows that the procedure is useful in ascribing photoemission peaks at particular binding energies of He(I) and He(II) spectra to the set of molecular orbitals.     

The halogenation of polycrystalline zinc studied by He(I)/(II) photoelectron spectroscopy

He(Iα)/(IIα) photoelectron spectra have been recorded for the surface reaction between clean polycrystalline zinc and molecular chlorine, bromine and iodine. For saturation exposures > 10⁻³ Pa a continuous layer of the ZnX₂ halide is formed. For low exposures < 2 × 10⁻⁴ Pa there is evidence for a precursor species which is assumed to be chemisorbed atomic halogen atoms formed by dissociative adsorption.     

The He(I) photoelectron spectra of amine N-oxides

The He(I) photoelectron spectrum of β-hydroxyethyldimethylamine N-oxide shows the degenerate pair of N-oxide ionic states to be shifted by 0.49 eV to higher ionization potential, relative to the non-hydrogen bonded system. The two bands remain nearly degenerate. The ionization of the hydroxy lone pair is shifted by > 0.6 eV to lower ionization potential. INDO calculations for the corresponding ionic configurations of a model system (NH₃O + H₂O) are compared with the experimental observations.