Manfred O. Krause

Determination of the K-LL Auger spectra of N2, O2, CO, NO, H2O, and CO2

A double‐focusing electrostatic electron spectrometer has been used to measure the K—LL Auger spectra resulting from electron impact for each of the elements in the gaseous molecules N2, O2, CO, NO, H2O, and CO2. An energy resolution of 0.09% full width half‐maximum was normally employed. A method for analyzing these complex spectra is described. It involves the identification of normal and satellite lines. The former are defined as arising from single electron ionization from the K shell without additional excitation followed by an Auger process in which one electron fills the vacancy while a second goes into the continuum, and where all the other electrons remain in their same orbitals. Satellite lines result when extra excitation occurs either in the initial formation of the K vacancy or in the subsequent Auger process. To aid in the identification of these satellite lines, auxiliary experiments have been performed such as the study of discrete energy losses in photoionization due to electron shake‐up,...

Total and partial atomic-level widths*

Total and partial atomic-level widths of the K-, L-, M-, and N-levels of the elements (covering Z up to 120 for K- and L-levels) are presented in graphic form. Graphs are based on theoretical predictions; total widths are natural level widths as governed by the rates of the various deexcitation processes for a single hole in that level. The drawings make possible, throughout the periodic table, a quick survey of the magnitude and trends of the total level widths, rates and yields of radiative, Auger, and Coster-Kronig processes,and widths of x-ray, Auger, and Coster-Kronig lines.

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.

Relative Abundances and Recoil Energies of Fragment Ions Formed from the X‐Ray Photoionization of N2, O2, CO, NO, CO2, and CF4

A specially designed mass spectrometer has been used to study the fragment ions following x‐ray photoionization of several simple gaseous molecules, containing only first‐row elements. Two photon sources were used: CuLα (930 eV) and CKα (280 eV). The higher‐energy x‐ray source produced initial vacancies primarily in the K shells of the different elements, while the lower‐energy radiation produced ionization entirely in the valence shells. Data were obtained as a function of collection voltage, and relative abundances of the fragment ions were evaluated under conditions of equal collection efficiency. From the shape of the collection efficiency curve the average recoil energies were estimated. The results are briefly discussed in terms of the effect of the KLL Auger processes and multiple ionization.

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.

The Mζ X rays of Y to Rh in photoelectron spectrometry

Abstract Widths, relative intensities and other parameters relevant to photoelectron spectrometry were determined for the Mζ lines of Y to Rh. Good photon sources are obtained with Y, Zr, and Nb. Use of an electron energy analyzer as a soft X-ray spectrometer of high resolution is demonstrated.

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.

K X-ray emission spectra of Mg and Al

Relative energies and relative intensities of the K alpha satellites and the K beta bands of Mg and Al metals and anodized Al have been measured. Spectra were obtained with a PAX spectrometer which provided high resolution and accurate intensity data (PAX identical to photoelectron spectrometry for the analysis of X-rays). Relative energies agree well with data from the literature. Relative intensities of line groups that correlate with initial KL, KL2 and KL3 defects are compared with theoretical predictions based on the shake-off theory. Theory underestimates the satellite group intensities by 15% for KL defects and 30-40% for KL2 defects. The intensity ratio K beta /K alpha 1,2 is found to be 1.7% for Mg and 2.4% for Al.