Timothy A. Whitley

Angle‐resolved photoelectron cross section of CF4

Partial photoelectron cross sections σ and angular distribution parameters β were obtained for the first five valence orbitals in CF4: 1t1, 4t2, 1e, 3t2, and 4a1, as a function of photon energy from 17 to 70 eV. These data were taken with the aid of angle‐resolved photoelectron spectroscopy and synchrotron radiation. The results were compared with earlier data on CCl4. Substantial differences were found. These are explained partly in terms of the absence of a Cooper minimum with a fluorine compound as opposed to the presence of a Cooper minimum with chlorine compounds and partly in terms of the position of shape resonances. Data on CF4 were also compared with recent calculations of Stephens et al., who used the multiple‐scattering Xα method. Structure in the photoelectron spectrum of CF4 lying on the low energy side of the third band was identified as due to autoionization and evidence is given as to its specific nature.

Angle resolved photoelectron spectroscopy of the valence shells in HI and CH3I as a function of photon energy from 13 to 90 eV

Angle‐resolved photoelectron spectroscopy was carried out on the valence shells of HI and CH3I over a photon energy range of 13–90 eV with the use of synchrotron radiation. From these data, partial cross sections and angular distribution parameters were obtained for bands corresponding to the 1 2Π and 1 2Σ+ states of singly ionized HI and the 1 2E, 1 2A and 2 2E states of singly ionized CH3I. Calculations were carried out on HI for the same parameters with the use of the multiple scattering Xα method. The results, both experimental and theoretical, are examined in terms of the Cooper minimum. Clear evidence for minima in both the cross sections and β values are found for the lone‐pair orbitals. Bonding orbitals involving the iodine 5p subshell also show minima in the energy dependence plot of the β values, but the effects are less pronounced. These results are compared with similar studies on chlorine‐containing molecules. The lone‐pair orbitals showed spin‐orbit resolved bands in the photoelectron spectr...

Angle-resolved photoelectron spectroscopy of HCl from a photon energy of 16 to 80 eV

Angle‐resolved photoelectron spectroscopy was performed on HCl using synchrotron radiation over a photon energy from 16 to 80 eV. The partial cross sections and angular distribution parameters β were obtained for photoionization of both the 2π and 5σ orbitals. Multiple scattering Xα calculations were also carried out for the cross sections and β values. The calculations, together with previously published results on the cross section using a Hartree–Fock model, were compared with experiment and gave reasonable qualitative agreement. Both experimental and theoretical results were examined with particular regard to the nature of the Cooper minimum, and the differences between the behavior of the minima for the two orbitals are discussed in detail.

Angle‐resolved photoelectron spectroscopy of N2O measured as a function of photon energy from 14 to 70 eV

Angle‐resolved photoelectron spectra have been taken of the first four bands of N2O, using photons from synchrotron radiation. From these data, the partial cross section and the angular distribution parameter β have been obtained over a range of photon energies from 14 to 70 eV for the first four valence orbitals: 2π, 7σ, 1π, and 6σ. Calculations, based on the multiple scattering Xα method, also have been performed to obtain the partial cross sections and β values for comparison with experiment. An important element in the understanding of these data is the presence of shape resonances particularly in the photoionization of the 7σ and 6σ orbitals. Although the calculations are not in good quantitative agreement with experiment, they are able qualitatively to give a correct account of the overall behavior. In the case of the photoelectron spectra of the 7σ and 6σ orbitals, the vibrationally resolved bands were studied independently, particularly for their β values. Evidence of autoionization was found from...

Systematic investigation of the Cooper minimum for the hydrogen halides

Angle‐resolved photoelectron spectroscopy has been carried out on the two outermost molecular orbitals of HBr using synchrotron radiation from a photon energy of 14 to 110 eV. Both partial cross sections σ and angular distribution parameters β have been determined experimentally. For comparison, calculations were also carried out on σ and β using the multiple scattering Xα method. Both the experimental and calculated results are discussed in terms of the Cooper minimum. Comparison is made with earlier results on HCl and HI and with results on the rare gases, which are isoelectronic with the hydrogen halides.

Angle‐resolved photoelectron spectroscopy of the valence orbitals of SiCl4 as a function of photon energy from 14 to 80 eV

Angle‐resolved photoelectron spectroscopy coupled with synchrotron radiation have been used to measure partial cross sections and angular distribution parameters, β, from a photon energy of 14 to 80 eV for SiCl4. Parallel to these measurements, calculations have been made using the continuum multiple scattering Xα method. The results have been examined, primarily in terms of the phenomena of the Cooper minimum and shape resonances. Minima in both the cross sections and β values were found for each of the first five orbitals of SiCl4: 2t1, 8t2, 2e, 7t2, and 7a1. These minima were examined for their energy positions and, in the case of the β values, the depth of the minimum. Shape resonances were calculated in the photoionization of each of the orbitals, and a number of experimental features due to shape resonances are identified. The results, both experimental and theoretical, are compared with earlier work on CC14.

Angle‐resolved photoelectron spectroscopy of Cl2 as a function of photon energy from 18 to 70 eV

Angle‐resolved photoelectron spectroscopy using synchrotron radiation has been carried out on gaseous chlorine as a function of photon energy from 18 to 70 eV. From this data the partial cross sections and angular distribution parameter β have been derived for the first three orbitals. For the lone pair orbitals 2πg and 2πu, distinct minima are found in both the partial cross sections and β values in the region of photoelectron energies from 30 to 40 eV. Less well‐defined minima are also seen in the case photoionization for the nonlone pair orbital 5σg. These features are believed related to the Cooper minimum that arises from an atomic 3p subshell. Calculations have also been carried out on the partial cross sections and β values using the multiple scattering Xα method. Comparison with experiment gives excellent qualitative agreement with regard to the ‘‘Cooper minimum.’’ The nature of the Cooper minimum in molecules and its usefulness in understanding photoelectron dynamics is discussed.

Photoelectron dynamics of the Cooper minimum in free molecules

The general properties of the Cooper minimum in molecules are reviewed. Experimental results from synchrotron radiation together with theoretical calculations are presented on both the partial cross sections and angular distribution parameters, β. A detailed examination of HCl is used as an example. Previously unpublished results on CClnH4−n, CClnF4−n, ethylene dichloride, I2 and ICl are included. The Cooper minimum is largely discussed as a perturbation from atomic behavior, and is examined as a function of atomic number. The Cooper minimum is also examined as a function of chemical environment. Finally, needs for future research are briefly described.

Autoionization in N2O as measured by angle‐resolved photoelectron spectroscopy

Angle‐resolved photoelectron spectroscopy has been carried out on N2O as a function of photon energy from 13.5 to 20.5 eV using monochromatized synchrotron radiation. The purpose of these studies has been to investigate autoionization, and most of the data have been collected under conditions of constant ionic state. Six resonances are discussed in detail: the first four that form a portion of several Rydberg series leading to the A 2Σ+ ionic state and the first two window resonances leading to the C 2Σ+ state. Data have been taken as a function of the final state vibrational band and as a function of angle between the ejected photoelectron and polarization vector. In particular, the correlation between the integrated angular intensity and its angular distribution parameter, β, has been measured as a function of photon energy over the resonances. The nature of these results and importance to the understanding of autoionization in molecules is discussed.

Characterisation and toxicity of water-soluble photooxidants produced during irradiation of coal liquids by sunlight☆

Abstract Four coal-derived oils, a No. 2 diesel fuel oil, and a petroleum crude oil were layered onto water in a closed, stirred vessel and were exposed to natural or artificial sunlight for periods up to 170h. Photooxidants which dissolved into the underlying water were quantified amperometrically. Concentrations of water-soluble photooxidants increased steadily beneath all coal liquids at 25% of the rate beneath diesel fuel; none were produced beneath irradiated crude petroleum. Characterisation of photooxidants by kinetics and thermodynamics of reaction with iodide indicated that hydrogen peroxide and organic hydroperoxides were produced under one coal liquid. Acute toxicities to Daphnia magna of the water before and after reduction of photooxidants with thiosulphate were consistent with these identifications. The results suggest that photooxidant production may enhance the toxicity of spilled coal liquids in rivers, particularly after the highly soluble phenols have been depleted from a floating oil film.