Photoelectron spectroscopic studies of the monomers and dimers of acetic and trifluoracetic acids

Comparison of the He(I) and He(II) photoelectron spectra of acetic and trifluoracetic acids has clarified the assignments of their p-based ionization potentials. The He(I) spectra of the gas-phase homodimer of each molecule have been observed using a high-pressure nozzle inlet system operating at room temperature. Spectrum-stripping of the monomer—dimer mixed-spectra gives dimer spectra which are interpreted with the aid of molecular orbital calculations. Appropriate mixtures of the two acids have been analyzed to obtain the He(I) spectrum of the 1:1 heterodimer. Assignments of the three dimer spectra indicate that the inductive influences of the methyl and trifluoromethyl groups are transmitted across the hydrogen-bond bridges.     

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.     

Valence shell photoionization spectra of some substituted hydroxy-acetylenes. A tentative correlation with their cyclotrimerization reactions

He(I) photoelectron spectra of a series of oxyacetylenes have been studied. The π_CC and oxygen “lone pair” IE's have been tentatively related to the chemical behaviour of these compounds. CNDO/2 calculations have been carried out on the three simplest molecules of the series.     

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.     

Ab initio calculation of the dipole moment of cyanamide

The He(I) photoelectron spectra of the isoelectronic series Fe(CO)₂(NO)₂, Co(CO)₃NO and Ni(CO)₄ are reported and interpreted by means of ab initio SCF-MO calculations. For the nitrosyl complexes it is found that ionization potentials calculated assuming Koopmans' theorem are seriously in error due to the considerably greater orbital relaxation accompanying ionization from metal than from NO valence orbitals. When such allowance is made for orbital relaxation by performing restricted Hartree-Fock (RHF) calculations on the ionic states, the experimental spectra are accurately reproduced and the observed similarity of the spectra of all three molecules is explained.     

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.     

The photoelectron spectroscopic characterization of vapors above heated alkali tetrafluoroaluminates,alkali tetrachloroaluminates,and ammonium tetrachloroaluminate

The high-temperature He(I) photoelectron spectra of gas-phase alkali tetrafluoroaluminates, alkali tetrachloroaluminates, and ammonium tetrachloroaluminate have been obtained. The identities of the vapor-phase entities were assigned from data derived by electron diffraction, mass spectrometry, and matrix-isolation and vapor infrared spectroscopies. The ionization energies observed in the spectra have been assigned molecular-orbital origins through the use of theoretical calculations and comparisons with analogous compounds.     

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.     

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.     

The photoelectron spectra of trimethylgermane,chloro- and fluoro-trimethylgermane

The He(I) photoelectron spectra of the series Mein3GeX (X = F, Cl, H) is reported. Assignments are proposed based on comparisons with spectra of similar compounds and on semi-empirical CNDO/2 calculations. The He(II) spectra were used to resolve some ambiguities.     

Optical reaction cross-sections for light projectiles

The optical reaction cross-sections forn, p,²H,³He,³He and⁴He for several global optical potentials available in the literature have been parametrized in terms of simple empirical expressions which are smooth functions of the target mass number and the projectile energy. The empirical forms are 5–10% accurate over the periodic table and energy-range upto 50 MeV. They can be conveniently used in calculations where the optical reaction cross-sections are required as input. The calculation of proton spectra in the (n, p) reaction at 14 MeV is discussed.     

The photoelectron spectra of methyl(bromo)germanes

He(I) and He(II) photoelectron spectra are reported for the series of bromides MeGeBr₃, Me₂GeBr₂ and Me₃GeBr. Assignments are based on semi-empirical CNDO/2 calculations, peak shapes and intensities. X-ray-excited spectra of the valence region were also utilized. Comparisons are drawn with the corresponding fluoride and chloride species.     

Angle-dependent valence photoemission from adsorbed molecular nitrogen a comparison of measurements and model calculations

He I and He II photoelectron spectra for N₂ adsorbed on W (110) have been measured at three different polar emission angles. The behaviour of the adsorbate-induced features with angle is compared to the angle- dependence of dipole matrix elements for oriented N₂, Ni-N₂, and Ni₉-N₂ clusters obtained by SCF-Xa-SW calculations. The agreement is very good for He I and acceptable for He II, if the N₂ axis is assumed normal to the “surface” and the assignment of peaks proposed earlier is used. For He II the use of the big cluster is important to arrive at good agreement.     

Photoelectron spectra of halides

High resolution photoelectron spectra, obtained with He I (584 Å) resonance radiation, are reported for ClF, ClF₃, BrF₃ and BrF (partial spectrum). In some cases Ne I (736–744 Å) radiation has also been used. Spinorbit and vibrational fine structure is resolved for the ground ²II states of ClF⁺ and BrF⁺; values obtained for ClF⁺ and ζ = 630 cm^-1, v′ = 870 cm^-1, and for BrF⁺ ζ = 2600 cm^-1, v′ = 750 cm^-1. From the vibrational envelope of the X ²∏ states, a bond length change of δr _e (-)0·10 Å for ClF⁺ and BrF⁺ is estimated. Ab initio SCF-MO calculations for ClF and ClF₃ are used to aid in the interpretation of the spectra via Koopmans' theorem. A considerable amount of charge delocalization in the trifluorides is inferred from the photoelectron spectra, and this is borne out by the calculations.     

Photoelectron spectra of fluorotribromomethane and fluorotrichloromethane

High resolution He(I) photoelectron spectra are reported for fluorotribromomethane CFBr₃ and fluorotrichloromethane CFCl₃. The assignments are based on CNDO/2 calculations, symmetry arguments, the fine structures of the bands, and comparison with the photoelectron spectra of related compounds. Linear relationships have been found between the Pauling electronegativity values for the halogen atoms and the observed vertical ionization energies corresponding to a₂ of a₂′ orbitals of CFX₃ and related compounds CHX₃, OPX₃, BX₃ and PX₃ (X = F, Cl, Br, I).     

Valence and C 1s core level photoelectron spectra of camphor

The valence photoelectron spectrum of camphor has been recorded with 95 eV synchrotron radiation, with better definition than previous He I spectra. The spectrum is interpreted by comparison with these He I results and with the aid of an outer-valence Green’s Function calculation of the orbital ionization energies. These calculations closely reproduce the observed vertical ionization energies in the outer valence region. A core level spectrum of the C 1s region (hν=357.9 eV) is also presented and reveals a marked shift of the carbonyl carbon relative to all others in the molecule.     

Photoelectron spectra of acetaldehyde and acetyl halides

The He I photoelectron spectra of acetaldehyde and acetyl fluoride, chloride and bromide have been obtained. The spectra are interpreted in terms of molecular orbital structures, by comparison with results for related molecules and by a consideration of the inductive and resonance effects. The results of CNDO/2 and INDO semi-empirical calculations are also reported. It is found that the oxygen “lone pair” is progressively stabilized as the electronegativity of the halogen increases. The vibrational structure of the first photoelectron band of acetaldehyde is compared with the observed structure of Rydberg transitions in the optical spectrum.     

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.