Frederick A. Grimm

Photoelectron Spectra of Methane, Silane, Germane, Methyl Fluoride, Difluoromethane, and Trifluoromethane

An electron spectrometer which employs double focusing electrostatic plates is described. The photoelectron spectra obtained by bombarding methane, silane, germane, methyl fluoride, difluoromethane, and trifluoromethane with 21.22‐eV photons are presented. The experimental ionization energies are compared with theoretical and other experimental data, and molecular‐orbital assignments are made for the energy values obtained. Broad double maximum bands were observed in the case of methane, silane, and germane and are discussed in terms of Jahn–Teller distortion for the positive ions. Possible correlation of the methane spectrum with interstellar space data is also discussed.

The photoelectron spectra of the tetrafluoro and tetramethyl compounds of the group IV elements

Abstract The photoelectron spectra of CF 4 , SiF 4 , GeF 4 , C(CH 3 ) 4 , Si(CH 3 ) 4 , Ge(CH 3 ) 4 , Sn(CH 3 ) 4 , and Pb(CH 3 ) 4 h

Use of the multiple‐scattering method for calculating the asymmetry parameter in the angle‐resolved photoelectron spectroscopy of N2, CO, CO2, COS, and CS2

Calculations based on the multiple‐scattering method have been performed for the asymmetry parameter (β) as a function of photon energy (from the ionization threshold to 2 Ry above threshold) for the gaseous molecules: N2, CO, CO2, COS, and CS2. For the diatomic molecules N2 and CO we have investigated the use of an overlapping spheres transition state model. The calculations were critically compared with experimental data in the literature. In addition, we have carried out angle‐resolved photoelectron spectroscopy on the five molecules using a polarized source of He(i) radiation. Although the calculations show in general good predictive capability, there are also several instances where these calculations seem inadequate and suggestions are made for future work.

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 CCl4: The Cooper minimum in molecules

Angle‐resolved photoelectron spectra have been taken for the first five orbitals in CCl4 (2t1, 7t2, 2e, 6t2, and 6a1) using a variable photon source extracted from synchrotron radiation. From these data, the partial cross sections and angular distribution parameters β have been determined for photon energies from 16 to 80 eV. In the case of the lone pair orbitals (2t1, 7t2, and 2e) minima in both the cross sections and β values were noted experimentally in the photon energy range of 40 to 50 eV. The behavior is similar in appearance to that observed with the 3p subshell of argon and is believed to be the molecular counterpart of the Cooper minimum in atoms. Calculations of the cross sections and β values have been made for each of the different orbitals of CCl4 measured experimentally using the multiple scattering Xα theory. Agreement between theory and experiment for the lone‐pair orbitals is qualitatively good and in the case of photoionization in the 2t1 orbital it has been possible to identify which c...

Angle‐resolved photoelectron spectroscopy of CO2 with synchrotron radiation

The angular asymmetry parameter β has been determined for the first four bands in the photoelectron spectrum of CO2 as a function of photon energy: X 2Πg(15–50 eV), A 2Πu(19–28 eV), B 2Σu+(19–28 eV), and C 2Σg+(21–67 eV). Use is made of a monochromatized beam of photons from the Wisconsin Synchrotron Radiation Center. The experimental results are compared with theoretical calculations employing the multiple scattering method and the overall agreement is good. In addition, the theoretical predictions for the effect on β of shape resonances have been verified except that the experimental widths are broader. This broadening has been partially accounted for in recent calculations of Swanson et al. by including the effects of vibrational motion. Finally, sharp changes in β as a function of vibrational level have been noted for the second and fourth electronic bands. Such behavior has been found for a variety of photon energies, and the results are examined against prevailing theory.

Angle resolved photoelectron spectroscopy of CS2 and COS measured as a function of photon energy from 21 to 70 eV

Data have been taken on both the partial cross sections and angular distribution parameters for the first five bands in CS2 with a photon energy from 21 to 70 eV and for the first four bands of COS from 21 to 40 eV. The results are compared with calculations based on the multiple scattering method. In the case of photoionization of the 2πg orbital of CS2 and the 3π orbital of COS, the experimental results and calculations have been successfully explained in terms of the Cooper minimum. The behavior of the fifth band of CS2 is accounted for by assigning it to a satellite peak arising from photoionization of the 2πu orbital by way of configuration interaction. Comparison between the experimental results and calculations showed some problem areas, particularly with regard to the prediction of shape resonances, and suggestions are made for future improvement of the calculations.

Photoelectron dynamics of the valence shells of benzene as a function of photon energy

Angle‐resolved photoelectron spectroscopy was carried out on the first nine valence orbitals of benzene using synchrotron radiation as a photon source. From these data cross sections σ and angular distribution parameters β were obtained over a photon energy of 10 to 34 eV. The experimental results are compared with calculations for the same parameters, based on the multiple scattering Xα method. Considering the complexity of the molecule, the comparison is gratifying. A number of shape resonances, which are predicted, have been identified experimentally. The orbital assignments for the photoelectron spectrum of benzene have been reexamined in view of the cross sections and angular distributions and have for the most part been verified.

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.