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 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.     

He(II) photoelectron spectra of the Group IVB tetrachlorides

He(II) photoelectron spectra of the Group IVB tetrachlorides MCl₄ (M = C, Si, Ge, Sn) are reported and compared with He(I) data. The discussion concentrates on the spectral intensity patterns and the nature of the additional structure revealed in the He(II) spectra.     

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.     

UV photoelectron spectra of the indium(I) and thallium(I) cyclopentadienides

Vapour-phase He I and He II photoelectron spectra of the cyclopentadienides of indium(I) and thallium(I) are reported. The discussion concentrates on the implications of the changes in band intensity that are observed on switching from He I to He II excitation, and on the nature of the additional structure revealed in the He II spectra.     

He(I)/He(II) photoelectron band intensity ratios for simple organic molecules

Band intensifies in the He(I) and HE(II) photoelectron spectra of some simple organic molecules (methanol, methylamine, formaldehyde, acetaldehyde, formic acid, acetic acid, methyl formate, ethylene, butadiene and methyl isothiocyanate) have been measured. The relative band intensity ratios for a number of ionizations from n and π orbitals are presented.     

He(I) photoelectron spectra of bis(β-diketonate)nickel(II) complexes and their mono- and di-thio analogues

The vapor-phase He(I) photoelectron spectra of a series of bis(β-diketonate) nickel(II) complexes and some mono- and di-thio analogues are reported. The spectra are discussed in terms of the metal-ligand bonding present, and the effect on this bond of replacing oxygen donor atoms by sulphur donor atoms.     

He(I) and He(II) populations in the Nagoya TPD plasma machine

A collisional-radiative model is used to explain the He(I) population densities observed by Otsuka, Ikee and Ishii in their TPD plasma machine. It is shown that a plasma model, which is partially optically thick to He(II) Lyman radiation, can explain the experimentally observed He(II) population density at T_e=3.17 eV. The agreement between the experimental and calculated He(II) population densities observed by Otsuka and others is shown to be due to an error in their calculations.     

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.     

The electronic structure of dinuclear transition-metal complexes containing metal—metal interactions: II. He(I) and He(II) photoelectron spectra of hexacarbonyldi-irondisulfur and related complexes

The He(I) and He(II) photoelectron spectra of a series of Fe₂(CO)₆LL¹-type complexes (L = L¹ = S, (i-propyl)S; L,L¹ = t-but of an all-electron, ab initio SCF MO calculation on Fe₂(CO)₆S₂ and of extended CNDO calculations on related molecules. Assignments given ar He(I)/He(II) intensity differences, and on comparison with related molecules.The coordination of the bridging ligands to the metal centres and the nature of the metal—metal interactions are discussed.     

On the He(I) and Ne(I) photoelectron spectra of OCS

The He(I) (58.43 nm) and Ne(I) (73.59–74.37 nm) photoelectron spectra of carbonyl sulphide have been reinvestigated at an improved resolution and a high signal-to-noise ratio; deconvolution of the data was carried out to aid interpretation of the spectra. Improved values are deduced for the vibrational wavenumbers and the ionization energies. The spin—orbit components of the Ã²Π II level are well resolved and a value of 135 cm^?1 (17 ± 5 meV) is proposed for the splitting. Perturbations in the relative intensities are observed in the Ne(I) spectrum; they suggest that the autoionizing Rydberg state located around 73.7 nm is excited by the 73.59 nm Ne(I) line and contributes to populate, with different probabilities, the ionic levels of lower energy, and particularly the X?²Π state.     

Population densities of He(I) and He(II) excited states in plasmas

Reduced population coefficients for He(I) and He(II) levels, both for optically thin and partially optically thick conditions, have been calculated from a collisional-radiative model using recent experimental and theoretical cross sections. The calculated population densities are compared with experimental results on helium plasmas. Agreement with experimental results is better at low electron temperatures.     

Measurement of Stark broadened profile of He(II) 4686A

Stark broadened profiles of the He(II) 4686A line were measured using a Z-pinch plasma as source. The electron density was determined from the halfwidth of the He(I) 3889 line and the temperature from the intensity ratio of the He(II) 4686 and the He(I) 3889 lines. The electron densities covered the range 0.5?2.3×10¹⁷ cm³ and the electron temperature was 4 eV. The plasma homogeneity was checked by varying the length of the column observed. The experimental profiles are in better agreement with the recent calculations of Greene than with the earlier calculations of Keeple.     

He(I) Photoelectron spectroscopy of transient species: fluorothiocyanate (FSCN)

Valence ionisation energies, obtained using He(Iα) photoelectron spectroscopy, of the hitherto unknown and unstable molecule FSCN are presented. Interpretation of the spectra is based on experimental considerations, correspondence with the spectra of related molecules, and the results of Hartree—Fock—Slater calculations using STF basis sets of double-zeta quality. The molecule is shown to exist in the thiocyanate form.     

Coordinative bond and d-shell ionisations in the UV photoelectron spectra of bis(β-diketonato) cobalt(II) and copper(II) complexes,and their thioanalogues

The analysis of UV photoelectron spectra of the title compounds, as well as of their Ni(II) analogues, is presented, with particular regard to the identification of d-ionisation bands. The spectra are assigned on the grounds both of a framework of interpretation similar to that usually applied to β-diketonato metal complexes, and of a systematic comparison between He(I) and He(II) data.     

The He(I) photoelectron spectra of some γ-substituted Co(III) acetylacetonate complexes

The He(I) photoelectron spectra of the complexes of Co(III) with acetylacetone and several derivatives are reported. The ionization potentials of metal-localized d-electrons and ligand π-orbitals are used to probe the extent of metal-to-ligand π-bonding and possible aromatic character in the chelate ring.     

UV and X-ray-excited photoelectron spectra of trifluoromethylgermanes (CF3)4−nGeHn(n = 1–3)

He(I), He(II) and X-ray-excited photoelectron spectra of the trifluoromethylgermanes (CF₃)_4?nGeH_n(n = 1–3) are reported. Assignments of the valence region are made on the basis of semi-empirical CNDO/2 calculations, comparisons with the spectra of related series of molecules, band shapes, and relative-intensity changes between features in the He(I) and He(II) spectra. Core-level binding energies are also compared with those of related species, and the usefulness of CNDO/2 and EESOP charge calculations is examined.     

He (Iα) photoelectron spectra of some higher aromatic perfluoro compounds

He(Iα) excited photoelectron spectra, the inferred ionisation energies, and their assignment, are presented for perfluoro-benzene, -naphthalene, -anthracene, -phenanthrene, -pyrene and -acenaphthylene.