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  • Electronic Resource  (11)
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  • Electronic Resource  (11)
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  • 1
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Journal of the American Chemical Society 117 (1995), S. 5417-5418 
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2701-2707 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Photoelectron spectra of the title molecules are reported at 3.49 eV photon energy. Vibrational structures are resolved in the spectra of FeC−3 and FeC3H−. The FeC−4 spectrum is unusually broad, indicating a large equilibrium geometry change from the anion to the neutral states. The FeC4H− spectrum exhibits a single strong feature. Theoretical studies using the density functional theory are carried out to determine the structures and bonding of these clusters. All the molecules in the anion ground states are found to be linear with the Fe atom bonded at one end. The Fe and C bonding involves strong Fe 4s and C sp interactions as well as considerable Fe 3d and C π interactions. The n=3 species can be best characterized by cumulenic types of bonding with FeC3H also having an acetylenic isomer. The n=4 species in the linear structures can be approximately described by diacetylenic types of bonding. Mulliken charge analyses indicate that the extra charge in all the anions enters mainly into the Fe 4s antibonding orbital, in agreement with the assignment that the threshold detachment takes place from the σ* orbital mainly between the Fe and C atoms. The vibrational structure resolved in the FeC−3 spectrum yields a Fe–C stretching frequency of 700 (150) cm−1 for the first excited state of FeC3, in agreement with the Fe–C multiple bonding character. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 11814-11817 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 9480-9493 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A higher resolution magnetic bottle photoelectron spectrometer for the study of the electronic structure of size-selected metal clusters is presented. The initial study on Fe−n (n=3–24) is reported at a photon energy of 3.49 eV. The photoelectron spectra of these clusters exhibit sharp features throughout the size range. The spectra for Fe−3–8 show large size dependence with many resolved features. The spectra for Fe−9–15 exhibit some similarity with each other, all with a rather sharp feature near the threshold. An abrupt spectral change occurs at Fe−16, then again at Fe−19 and Fe−23. These photoelectron spectral changes coincide remarkably with changes of the cluster reactivity with H2. Extended Hückel molecular orbital (EHMO) calculations are performed for all the clusters to aid the spectral interpretations. The calculations yield surprisingly good agreement with the experiment for clusters beyond Fe9 when body-centered cubic (bcc) structures are assumed for Fe9–15 and a similarly close-packed structure with a bcc Fe15 core for the larger clusters. The EHMO calculations allow a systematic interpretation of the sharp photoelectron spectral features in Fe−9–15 and reproduced the abrupt spectral change taking place from Fe−15 to Fe−16. Most importantly, the reactivity changes of the clusters with H2 are successfully explained based on the detailed electronic structures of the clusters, as revealed from the photoelectron spectroscopy (PES) spectra and the theoretical calculations. The calculations also correctly predict the existence of magnetism in these clusters and yield reasonable values for the cluster magnetic moments. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8277-8280 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study Ge2O2 and Ge2O−2 with density functional theory (DFT) and photoelectron spectroscopy (PES). We find that Ge2O2 is a rhombus (D2h), closed-shell molecule with a large HOMO-LUMO gap. The PES spectrum of Ge2O−2 is obtained at four detachment photon energies: 1064, 532, 355, and 266 nm. Vibrational structure is resolved at the lowest photon energy with a single progression and a frequency of 400 (60) cm−1. The experimental adiabatic electron affinity is obtained to be 0.625 (0.050) eV for Ge2O2. The calculated vertical and adiabatic electron affinities and the HOMO-LUMO gap are in good agreement with the experimental values. The calculated totally symmetric vibrational mode of Ge2O2 (335 cm−1) is in reasonable agreement with the observed vibration and represents a Ge–Ge breathing motion. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8714-8717 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photoelectron spectra of FeO− and FeO−2 are obtained at 3.49 eV photon energy. Transitions to the ground state (5Δ) and three low-lying excited states (5Σ+, 3Σ+, and 3Δ) of FeO are observed. The two low-spin excited states found at 6770 and 8310 cm−1 above the ground state, respectively, have not been observed before. The two Σ states, characteristic of detachment of a nonbonding electron from the FeO− anion, exhibit no vibrational progressions while a vibrational progression is observed for each of the two Δ states. The two high-spin states 5Δ and 5Σ+ are in agreement with a previous photoelectron study [P.C. Engelking and W. C. Lineberger, J. Chem. Phys. 66, 5054 (1977)]. The 3Δ state has a vibrational frequency of 800 (50) cm−1. The spectrum of FeO−2 only shows one major feature with little vibrational structure at this photon energy. The electron affinity of FeO2 is determined to be 2.358 (0.030) eV. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 80 (1993), S. 1257-1261 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new method has been developed to measure properties of equilibrium, or thermal, defects in intermetallics using the technique of perturbed angular correlations of gamma rays (PAC). After quenching, thermal defects are detected microscopically by distinctive nuclear hyperfine interaction signals produced when they localize next to probe atoms present in high dilution. Using a Schottky defect model and applying the law of mass action to defect equilibria, a linear Arrhenius temperature dependence is predicted for a “normalized” monovacancy site fraction. We have observed such linear dependences in PAC experiments on NiAl, CoAl and TiAl using the111In probe. Features of the method are summarized, of which the most important are the abilities to discriminate between different defects and to determine absolute vacancy concentrations, formation enthalpies and entropies. Extremely large formation entropies have been obtained for NiAl, CoAl and TiAl, suggesting vacancy concentrations of ∼ 15% at the melting temperatures.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 79 (1993), S. 745-748 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Site fractions of dilute111In/111Cd probe atoms in different lattice locations in quenched, equi-atomic TiAl are measured using perturbed angular correlations of gamma rays (PAC). The vacancy-free substitutional site fraction, observed via its nuclear quadrupole interaction, is observed to decrease with increasing quenching temperature, reflecting an increase in the thermal defect concentration. Assuming that the thermal defect is the Schottky defect, the law of mass action, and a binding energy of 0.2 eV between vacancies and the In probe, the experimental temperature dependence is analysed to yield a formation enthalpy of 4.7(4) eV and entropy of 25(4)k B for the Schottky defect. The vacancy concentration on one sublattice is given in terms of these parameters by the expression [v]=exp(S F/2k B) exp(−E F/2k B T), and is found, for example, to have the value 1.4% at 1350°C, a large value.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In previous work, we introduced hydrogen (H) into Ni and Pt metals at room temperature by electrolysis. To study H-vacancy interactions on an atomic scale, trapping of diffusing H atoms at impurity-vancancy complexes was detected using perturbed γ-γ angular correlations. Two new results are reported here: (1) Transformation rules are clarified between undecorated and H-decorated complexes which are detected after annealing Pt at 323 K. In addition, non-cubic In sites were observed to form by chargingannealed, Pt, which are attiributed either to H atoms at random in the lattice or to precursor nuclei of a Pt hydride. (2) NiH is observed to form under cathodic charging of Ni at high current densities, and detected by growth of a nonmagnetic, cubic metastable phase.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Hyperfine interactions 60 (1990), S. 655-658 
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Perturbed γ-γ angular correlation spectroscopy was applied to study the structure and properties of point defects near111In probes in quenched and annealed NiAl samples with five compositions in the range cNi=48–52%. Quadrupole interaction signals are analysed in terms of near-neighbor Ni-vacancy and nextnear-neighbor Ni antisite atom defects. Large mono- and divacancy concentrations were observed in all samples after quenching. For cNi〈50%, the vacancy defects could not be annealed out (structural defects). For CNi〉50%, large quenched-in vacancy concentrations annealed out near 500°C. For cNi=50%, most vacancies annealed out near 500°C, but about 35% of the111In probes retained a trapped monovacancy. This is attributed to a very low value of the formation enthalpy of a vacancy next to the In probe, estimated to be 0.16(2) eV. A lesser annelaing stage detected at 300°C is tentatively attributed to diffusion of Al-vacancies.
    Type of Medium: Electronic Resource
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