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  • 1
    Electronic Resource
    Electronic Resource
    On the electronic structure of electrides (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 5875-5882 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We explore a mechanism for the remarkable charge isolation of the localized, or trapped, electrons found in the crystalline electrides Cs(18C6)2 and Cs(15C5)2. 133Cs NMR measurements show only ≈ 0.05% atomic character of the spin density at the Cs nucleus, consistent with many features of the structure and measured properties which indicate that the localized electron distribution is centered at the anion vacancies. The optical absorption data suggest that the localized electrons, which give rise to the Curie-law spin susceptibility, must penetrate appreciably into the crown ethers, (18C6) and (15C5), which encapsulate the Cs. We suggest that the large reduction of the spin density at the Cs nucleus is due to a Coulomb barrier resulting from negative charge on the oxygens. A crude model, one electron moving in two spherical charged shells surrounding the Cs core, illustrates the mechanism and accounts accurately for the ratio of spin densities at the Cs nucleus found in the 18C6 and the 15C5 electrides. Hartree–Fock calculations for an idealized model of an isolated Cs(18C6)2 molecule, namely Li(9C3)2, tend to support the mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459584
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  • 2
    Electronic Resource
    Electronic Resource
    Photochemistry of adsorbed molecules. III. Photodissociation and photodesorption of CH3Br adsorbed on LiF(001) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1475-1497 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Submonolayers of CH3Br physisorbed on a LiF(001) surface were irradiated by pulsed ultraviolet (UV) in ultrahigh vacuum in a study of surface aligned photochemistry (SAP). Translational energy and angular distributions were obtained for both photofragments and photodesorbed molecules by angularly resolved time of flight to a mass spectrometer. Single-photon adsorbate photolysis (PDIS) led to photofragment distributions, CH3 and Br, which differed from gas-phase photolysis. Photodesorption (PDES) of CH3Br was nonthermal and arose from UV absorption by the LiF crystal. The dynamics for these photoprocesses were found to vary in an informative way with the coverage and the phase of the adsorbed layer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455148
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  • 3
    Electronic Resource
    Electronic Resource
    Photochemistry of adsorbed molecules. IV. Photodissociation, photoreaction, photoejection, and photodesorption of H2S on LiF(001) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 1498-1523 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The UV surface-aligned photochemistry (SAP) of submonolayers of H2S physisorbed on LiF(001) has been examined. Translational energy and angular distributions for photodissociation products and for H2S molecules leaving the surface after pulsed laser irradiation at 193 and 222 nm were measured by angularly resolved TOF to a quadrupole mass spectrometer. Single photon surface-aligned photodissociation (PDIS) of adsorbed H2S produced H with structured translational energy distributions P(ET) indicative of vibrational excitation within the complementary SH fragments. The SH vibrational distribution was bimodal and varied markedly with H2S coverage. Photoreaction (PRXN) within the adsorbate layer occurred as the H2S coverage increased beyond ∼0.1 monolayer. Molecular hydrogen was produced by PRXN of H with adjacent H2S(ad) molecules. The product H2 translational energy distribution showed evidence of both direct and indirect PRXN dynamics. At coverages greater than one monolayer, photoejection (PEJ) of H2S molecules with translational energies up to several eV was observed; PEJ was thought to be due to interadsorbate quenching of electronically excited H2S. At all the coverages examined, absorption of UV by the LiF substrate was found to photodesorb (PDES) H2S molecules with low translational energies (0–0.5 eV). The PDES was ascribed to an acoustic wave produced by laser excitation of color centers in the LiF, which were seen to fluoresce.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455716
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  • 4
    Electronic Resource
    Electronic Resource
    Surface-enhanced photodissociation: UV photolysis of OCS on LiF(001) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4092-4093 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453811
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  • 5
    Electronic Resource
    Electronic Resource
    Electron affinities in the self-interaction-corrected local spin density approximation (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 2849-2853 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron affinities are calculated for first- and second-row atoms in the self-interaction-corrected local spin density approximation (SIC-LSDA). We compare results obtained by the orbital SIC method of Perdew and Zunger to those obtained by a new method which employs orbital SIC for exchange and Stoll's spin-density SIC for correlation. The latter method exhibits exceptional accuracy in correlation and total energy for neutral atoms and negative ions. The orbital SIC method yields more accurate electron affinities overall. This represents a significant improvement over earlier results which employed a spherical approximation for the orbital densities. Both methods follow the experimental trends closely and yield results within 0.2 eV of experiment. This accuracy is shown to be the result of a striking cancellation of errors between exchange and correlation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452036
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  • 6
    Electronic Resource
    Electronic Resource
    The effect of reagent rotation on chemical reactivity: F+H2 revisited (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 6906-6918 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical trajectory calculations on the gas phase reaction F+H2 ( j)→HF+H have been carried out. Different reactivity trends were seen depending on whether there was a chemically significant and anisotropic well in the entrance channel of the potential surface. For those in which there is no such well, rotation may decrease reactivity at low values of j, but increases it thereafter. The reaction cross section SR ( j) decreases slowly from j=0, reaching a minimum near j=6 then increases again. This behavior has been reported for several systems, including H+H2, and seems to be the "canonical'' behavior for SR ( j) for most direct chemical reactions. For F+D2 the minimum does not occur until j=8. However, this does correspond to the same amount of rotational energy as the minimum for F+H2 . For potentials in which there is a deep anisotropic well, it is found that the j=0 results are dominated by the presence of the well, and that the SR ( j=0) is anomalously high. On such surfaces there is normally a sudden drop in cross section from j=0 to j=1, followed by an increase. The experimental findings of Lee's group [J. Chem. Phys. 82, 3045 (1985)] that the cross section increases on going from j=0 to j=1 probably precludes the possibility of a chemically significant well in the entrance valley. The rotational product state distribution for both types of potential is dominated by kinematics away from threshold, and does not show the same trends as the reaction cross section. The mean product vibrational quantum number 〈v'〉 can decrease at low j, then increase at higher j. This occurs only at collision energies close to threshold, and on potentials which have a tight bend force constant at the transition state. The more general case for this reaction is that 〈v'〉 increases with j. For the case in which the potential has no well the differential cross section shows precisely the same trends as does SR( j). All these trends can be explained using a simple model we have recently proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457359
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of reagent rotation in the reaction OH( j)+H2( j')→H2O+H (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7424-7433 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical trajectory calculations on the reaction OH( j)+H2( j')→H2O+H have been carried out with j≤40 and j'≤15 on both the Schatz–Elgersma [Chem. Phys. Lett. 73, 21 (1980)] and the Rashed–Brown [J. Chem. Phys. 82, 5506 (1985)] potential energy surfaces. When there is no rotation in the OH, then a plot of reaction cross section, SR( j') resembles that for an atom–diatom system: Just above threshold, rotation decreases reactivity for small j', but increases it for high j'; at higher translational energies this trend is less obvious, but still present. When j'=0, then SR( j) is a complicated function, decreasing for low j, then climbing to a maximum, finally decreasing once more at very large values of j. We have also carried out calculations with isotopically substituted H in OH, and show that these effects scale as the mass of the hydrogen isotope. We show that this behavior is due to artifacts in both the potential surfaces. Using a simple model we are able to rationalize this behavior. Using this same model, together with a potential in which the artifacts are absent, we predict that rotation in OH will decrease reactivity rather less than was reported in previous trajectory studies [Schatz, J. Chem. Phys. 74, 1133 (1981); Rashed and Brown, J. Chem. Phys. 82, 5506 (1985)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454306
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of OH rotation on the reaction OH(v=0, j)+H2→H2O+H (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 3698-3699 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The reaction cross section for OH(v=0, j≤31)+H2→H2O+H has been calculated using quasiclassical trajectories at E=0.15, 0.20, and 0.30 eV. There is an initial increase in reactivity with j, probably due to long-range R→T transfer. At very high j, the cross section decreases, probably because of disruption of the transition state by the OH rotation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452968
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  • 9
    Electronic Resource
    Electronic Resource
    Analytic energy gradients for general coupled-cluster methods and fourth-order many-body perturbation theory (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 5143-5150 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Energy gradient equations are presented for the coupled-cluster model with all possible excitations. By taking advantage of the equations for the coupled-cluster amplitudes, the gradient formulas may be expressed without explicit reference to the first-order changes in the amplitudes, in contrast to all earlier work. The coupled-cluster doubles (CCD) and coupled-cluster singles, doubles, and triples (CCSDT) models are treated as special cases of the general theory. Finally, by limiting the model to finite orders in perturbation theory, the gradient equations for the full fourth-order many-body perturbation energy are derived. Like the fourth-order energy itself, the gradient procedure is shown to be an n7 process in the number of basis functions. The computational implementation of this fourth-order energy gradient is discussed in detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451823
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  • 10
    Electronic Resource
    Electronic Resource
    Third-order MBPT gradients (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4379-4380 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448832
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