J. Wayne Rabalais

Trapped electrons in substoichiometric MoO3 observed by X-ray electron spectroscopy

Abstract Substoichiometric amorphous thin films of MoO3 in both the transparent and absorptive forms have been studied by X-ray electron spectroscopy. The transparent films can be colored blue (absorptive) electrically or by UV irradiation. The electron distribution curve of the blue film exhibits a small band near the Fermi edge which is absent in the transparent sample. This new band is attributed to electrons trapped in positively charged anion vacancies in the substoichiometric MoO3 lattice. This model provides an interpretation of the electrical conductivity and color of the films.

Electronic structure of tungsten carbide and its catalytic behavior

Abstract The different observations concerning the platinum-like electronic structure found in X-ray photoelectron spectra as contrasted by the platinum-unlike density of states detected by soft X-ray appearance potential spectroscopy is reconciled. The platinum-like catalytic activity of WC results from changes in the electron distribution when C is added to W; core level chemical shifts indicate electron transfer from W valence orbitals to C 2p orbitals.

Electronic structure of amino acids and ureas

Abstract The outer electronic levels of glycine, alanine, glycine ethyl ester, urea, and thiourea have been investigated by means of photoelectron spectroscopy using He I (584 A) and He II (304 A) radiation and CNDO/2 molecular orbital calculations. In the amino acids the molecular orbital (MO) ordering ha been found to be [σ core and carbonyl π > a″(O) a′(O) > a″(N)] with a first ionization potential of ∼8.8 eV. Glycine and alanine are foun to exist as the undissociated amino carboxylic acids rather than zwitterions in the high temperature vapor. In urea the three lowest energy molecular o are near-degenerate [σ(4b 1 ) ∼ π(1a 2 ) ∼ π(2b 2 )] while in thiourea only the two lowest energy MOs are near-degenerate [π(1a 2 σ(4b 1 ) ∼ π(2b 2 )]. The first ionization potentials of urea and thiourea are 9.7 and 7.9 eV respectively.

Calculated photoionization cross sections and relative experimental photoionization intensities for a selection of small molecules

The general equations for calculating photoionization cross sections of polyatomic molecules in the plane‐wave and orthogonalized plane‐wave approximations have been programmed for the electronic computer. Applications are described for the molecules H2, CH4, N2, CO, H2O, H2S, and H2CCH2 for incident photon energies from threshold to 1500 eV. Relative experimental photoionization band intensities for the above molecules are measured using NeI, HeI, and HeII resonance radiation. A simplified analysis of the intensities derived from electrostatic deflection analyzers is presented. The 2P3/2:2P1/2 intensity ratios of the rare gases are determined with the three modes of excitation mentioned above. An analysis of the resolution capabilities of an electrostatic deflection spectrometer as a function of electron kinetic energy is presented. Relative experimental photoionization band intensities for the above molecules obtained by ionization with the three uv sources and MgKa and A1Ka x‐ray sources are compared w...

Electronic states of C2H6

The complete photoelectron spectrum of ethane has been measured in the valence region using Ne, He I, and He II resonance radiation. The resolution of these spectra is sufficient to partially resolve vibronic structure accompanying the transition to the ground ionic state. The similarity of this structure with that obtained from model calculations using the Jahn-Teller theorem strongly suggests that the active vibration in this transition is a doubly degenerate CH3 deformation mode and that the ground ionic state is a Jahn-Teller split 2 E g state. These experiments suggest a 2 A 1g term for the first excited ionic state. The transition to the 2 A 2u state of the ion contains evidence for two active vibrations v 1 (C–H stretch) and v 3 (C-C stretch).

Model for calculating spin‐orbit interactions with applications to photoelectron spectroscopy

A semiempirical model has been developed for estimating spin‐orbit interactions in molecular ion states derived by ionization of closed‐shell neutral molecule states. A perturbation approach is used with an effective spin‐orbit interaction operator Hso and approximate Mulliken‐Wolfsberg‐Helmholz molecular orbital (MO) wavefunctions. Effective spin‐orbit parameters ζv were obtained by interpolation with respect to atomic charges derived from the MO calculations. The He I photoelectron spectra of the PX3(X = Cl, Br, I) and PYX3(X = Cl, Br; Y = O, S) series have been measured. Splittings observed in some of the ionization bands of this series have been successfully interpretated as spin‐orbit splittings using the newly developed model.

Photoelectron and electronic absorption spectra of SCl2, S2Cl2, S2Br2 and (CH3)2S2

Abstract Photoelectron and electronic absorption spectra of SCl 2 , S 2 Cl 2 , S 2 Br 2 , and (CH 3 ) 2 S 2 have been measured and analyzed. Quantum chemical calculations (CNDO/ 2 and MWH (Mulliken-Wolfsberg-Helmholtz) have been carried out and the electronic structures have been described in terms of molecular orbital theory. The variation in differential photoionization cross-section as a function of incident photon energy and results of MO computations are used to identify ionization bands and assign ground state MO configurations. Suggested ground state electronic structures coupled with computed virtual MOs are used to interpret the visible and near-ultraviolet electronic absorption spectra. The low energy excited states are described as molecular states followed by the initial members of Rydberg series. Calculated oscillator strengths for molecular transitions are in good agreement with those observed experimentally. Quantum defects, δ, for the Rydberg states have been calculated from the Rydberg equation using the adiabatic first ionization potential.

Photoelectron spectrum and ground state electronic structure of chromyl chloride vapor

Abstract The electronic structure of chromyl chloride CrO2Cl2 has been investigated by ultraviolet (HeI) photoelectron spectroscopy. Mulliken-Wolfsberg-Helmholtz molecular orbital calculations have been performed in order to provide a model for interpretation of the photoelectron spectra and to assist in assigning the low-energy optical absorption and emission transitions. The first ionization potential of CrO2Cl2 at 11.8 eV is due to ionization of the near-degenerate oxygen and chlorine nonbonding 2a2, 4b1, and 4b2 MOs. The first unoccupied orbital is basically a chromium dπ* orbital. The excitations (2a2, 4b1, 4b2)→ 7a1* correlate well with the three low energy absorption transitions observed.

Electronic structure of N,N-dimethylnitramine and N,N-dimethylnitrosamine from X-ray and UV electron spectroscopy☆

Abstract The electronic structure of N,N-dimethylnitranine. (CH3)2NNO2, and N,N,-dimethylnitrosamine, (CH3)2NNO, has been investigated through the use of electron spectroscopy and quantum chemical methods. Experimentally, the electron spectra of (CH3)2NNO2 and (CH3)2NNO were measured in the valence region on the gas phase molecules using UV (HeI and He II) radiation and in the valence and core regions on the solid materials (frozen at 170 K) using X-radiation (AlKα). Theoretically, the results of INDO and MWH Extended Hucket MO calculations are used for spectral interpretation. The semi-empirical potential model of Ellison is used for predicting is chemical shifts. The results of this investigation exemplify how the UV and X-ray electron spectroscopy techniques are symbiotic and how application of the two techniques along with the use of quantum chemical methods provide unique information about electronic structures.

Molecular photoionization cross-sections and their dependence on excitation energy☆

Abstract A general formula for the photoionization cross-section of a linear molecule in terms of atomic subshell cross-sections and diffraction effects is given. Example calculations are carried out for line intensities of CO and N 2 as a function of incident photon energy from threshold up to the soft X-ray region. The importance of associating CNDO coefficients to orthogonal Slater AOs is pointed out. General rules for dependence of photoionization cross-sections on excitation energy are discussed.