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  • 1
    Electronic Resource
    Electronic Resource
    A molecular orbital study of bonding and ionization energies in pentavalent uranium imide/amide complexes (1992)
    s.l. : American Chemical Society
    Inorganic chemistry 31 (1992), S. 577-581 
    Details
    ISSN: 1520-510X
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ic00030a010
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  • 2
    Electronic Resource
    Electronic Resource
    Partial cross sections in the photoionization of open-shell atoms: Photoelectron spectroscopy of Te (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 321-330 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A general expression is derived for the relative partial cross sections for formation of fine structure states in the photoionization of open-shell atoms. The expression is particularized to the cases of chalcogen and pnicogen atoms. By utilizing spectroscopic parameters, branching ratios from photoionization of the ground state, or other components of the lowest configuration, are predicted. New experimental data on atomic tellurium are reported, and compared with predicted branching ratios. The good agreement provides support for the calculational method, since this element is best characterized by intermediate coupling, and the intensities depart significantly from L–S based statistical weights. The comparative study of the pnicogen atoms is less revealing. Most of the intensity is concentrated in the triad 3P0,1,2, where experimental data suffer from limited resolution. A weak 1D2 peak is predicted for bismuth, where it has been observed, and for antimony, for which the relevant data are not yet available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460400
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  • 3
    Electronic Resource
    Electronic Resource
    The fine and magnetic hyperfine structure of 87SrF in its X 2Σ+ state (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5533-5538 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular beam rf–optical double resonance experiment was performed on 87SrF in its naturally occurring abundance ratio. The natural occurring abundances of the strontium isotopes are 86Sr (9.8%), 87Sr(7.02%) and 88Sr (82.5%). Numerous magnetic dipole allowed transitions between ρ-doublets in the X 2Σ+ state were measured to an accuracy of 3 kHz. The observed spectra were analyzed in terms of an effective Hamiltonian which includes the magnetic hyperfine and electric quadrupole interactions arising from the 87 Sr (I=9/2) and 19F (I=1/2) nuclei. The extracted spectroscopic hyperfine parameters were interpreted in terms of a simple molecular orbital picture for the electronic nature of the X 2Σ+ state. A comparison is made to previous results for the more abundant 86SrF and 88SrF isotopic forms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459622
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  • 4
    Electronic Resource
    Electronic Resource
    Charge distributions and valency in copper oxide crystals related to superconductivity (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 2983-2992 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present an overview of the discrete variational method for calculating orbital states of a molecular cluster in the local density approximation. Then we introduce a new method of embedding a finite molecular cluster in a crystal lattice. This new technique of cluster weighting is based on the bulk stoichiometry of the crystal and the Mulliken populations for chemically complete atoms—those atoms that have all their covalently bonded nearest neighboring atoms also in the cluster. We have applied our new approach to calculate linear-combination-of-atomic-orbitals ground states for seven copper oxide crystals and Cu metal. The average net Mulliken charges calculated for Cu atoms in this way are shown to correlate well with the observed energies of the Cu K edge feature in x-ray absorption spectra of these materials. Several of these compounds are important to understanding the high Tc superconductivity of copper oxides.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456919
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  • 5
    Electronic Resource
    Electronic Resource
    Interpretation of photoelectron spectra for ThF4, UF4, ThCl4, and UCl4 in terms of relativistic local-density molecular orbital calculations (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2928-2939 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We describe fully relativistic calculations for the actinide tetrahalides UF4, ThF4, UCl4, and ThCl4 using the Dirac–Slater local-density model. We use an extended basis set of numerical atomic functions calculated in a potential well. A multipolar expansion technique is used to represent detailed features of the molecular charge density and the local exchange potential used is the Von Barth–Hedin–Lundqvist potential. By describing the molecules with physically reasonable wave functions and charge densities, we are able to calculate transition-state energies in good agreement with most features of the experimental photoelectron spectra. For the chlorine 3s levels we suggest revised ionization energies in the gas phase. The experimental values in the literature seem to have been incorrectly assigned, probably because they occur near the high energy limit for He(I) radiation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459815
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  • 6
    Electronic Resource
    Electronic Resource
    A systematic analysis of the spectra of the lanthanides doped into single crystal LaF3 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 3443-3457 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The optical spectra of the lanthanides doped into single crystal LaF3 have been interpreted in terms of transitions within 4f N configurations. Energy matrices combining free-ion terms with a crystal field for an approximate model which assumes C2v instead of the actual C2 site symmetry were diagonalized. Excellent correlations were obtained between experimental transition energies and the computed level structures. We also report the results of previously unpublished experimental spectroscopic investigations of Nd3+ and Sm3+:LaF3, as well as predicted energy levels for Pm3+:LaF3. The spectroscopic data for each ion were independently interpreted using an effective-operator model, then the model parameters were intercompared. Systematic trends have been identified, and a comprehensive energy level diagram is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455853
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  • 7
    Electronic Resource
    Electronic Resource
    Crystal-field excitations and superconductivity in Nd1+xBa2−xCu3O7 (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4536-4538 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The f-electron excitation spectra of Nd ions in superconducting NdBa2Cu3O7 and semiconducting Nd1.5Ba1.5Cu3O7 have been determined by inelastic neutron scattering. Transitions within the paramagnetic ground-state multiplet due to crystal-field splittings have been observed up to about 120 meV in these materials. The temperature dependence of the width of the low-lying transition at ∼21 meV shows significant differences in the superconducting and normal states. Adopting the CF level assignments for HoBa2Cu3O7, we rescaled the CF parameters to account for the larger radial wave functions of Nd3+ ions and obtained a level scheme for the Nd using the lowest 100 states of the f3 configuration. The calculated level structures for REBa2Cu3O7 (RE=Nd, Pr, Ho) are in good agreement with neutron and susceptibility measurements. Influence of superconducting ordering on crystal-field transitions in the Nd1+xBa2−xCu3O7 system is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344860
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  • 8
    Electronic Resource
    Electronic Resource
    Neutron inelastic experiments on actinide dioxides: Search for crystal-field levels in NpO2 (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 3598-3600 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Early experiments at the pulsed neutron source at Argonne National Laboratory (ANL) showed that it was possible to observe crystal-field (CF) levels at energy transfers above 150 meV in UO2. More recent investigations at the UK pulsed source at Rutherford Laboratory have improved the resolution and seen a series of well-resolved peaks. Based on these measurements the CF parameters are V4=−130 meV and V6=+30 meV. Since these parameters should be independent of the precise An ion, there is interest in looking at the tetravalent oxides UO2, NpO2, and PuO2. We have now performed experiments at ANL on NpO2 at temperatures between 15 and 200 K. We find no sharp peak in the excitation spectrum up to energy transfers of about 250 meV. This result is contrary to the expected strong transition at about 53 meV using the above CF parameters in a complete intermediate coupling calculation. The observed phonon spectrum of NpO2, in comparison with that of ThO2, shows larger widths in all of the three vibrational bands above ∼30 meV, which may indicate strong interaction between CF levels with optic phonons in NpO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.340706
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  • 9
    Electronic Resource
    Electronic Resource
    f-electron localization/delocalization phenomena in PrBa2Cu3O7 and related compounds (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5067-5069 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In order to investigate possible mechanisms for the suppression of superconductivity in PrBa2Cu3O7 and CmBa2Cu3O7, the electronic properties of the Pr-compound have been examined using magnetic susceptibility and inelastic neutron scattering. These results are compared with those obtained on an insulator, PrScO3, chosen as a model compound. These experiments, together with cluster calculations, lead to the conclusion that an interaction between the f electrons and the Cu d electrons occurs in both PrBa2Cu3O7 and CmBa2Cu3O7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344672
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  • 10
    Electronic Resource
    Electronic Resource
    Self-consistent Dirac-Slater calculations for molecules and embedded clusters (1984)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 25 (1984), S. 185-200 
    Details
    ISSN: 0020-7608
    Keywords: Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The basis of self-consistent local density theory used in the fully relativistic Dirac-Slater model is briefly reviewed. Moment-polarized extensions of theory are developed to treat open-shell systems by lifting the pair-wise Kramers degeneracy. The discrete variational method is used to calculate one-electron energies and charge and magnetization densities of a series of rare-earth trihalides. The theoretical binding energies compare very well with recent gas-phase photoelectron spectra of Berkowitz et al. The von Barth-Hedin exchange and correlation potential produces energies which are significantly better, compared to simpler exchange-only models. Embedded molecular cluster studies on actinide compounds are reported, with particular emphasis on the AcO2 dioxides. Single-particle energy densities of states (DOS) and magnetization DOS are presented, along with an analysis of effective atomic configurations in the solid. Trends in these quantities with actinide atomic number are noted. In contrast to the semicore nature of rare-earth 4f electrons, the actinide 5f levels are seen to be active participants in bonding interactions.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560250115
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