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  • 1
    Electronic Resource
    Electronic Resource
    Dodecahedral and smaller arsenic clusters: Asn, n=2, 4, 12, 20 (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 2261-2266 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio all-electron quantum mechanical methods, including the Hartree–Fock (HF), second-order perturbation theory, configuration interaction with single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD) methods, have been applied to four arsenic clusters, diatomic As2, tetrahedral As4, cagelike As12 belonging to the D3d point group, and dodecahedral As20. Several basis sets were used. The double-zeta plus polarization (DZP) includes both d and f polarization functions, while the triple-zeta plus double polarization basis includes two sets of f functions on each atom. From the most reliable theoretical results, As12 is energetically lowest among the clusters considered, and As20 is energetically comparable to As4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467666
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  • 2
    Electronic Resource
    Electronic Resource
    The silyl anion (SiH−3): Harmonic vibrational frequencies and infrared intensities predicted at the SCF, CISD, and CCSD levels of theory with substantial basis sets (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8098-8104 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio quantum mechanical methods have been applied to obtain harmonic vibrational frequencies and infrared intensities for the silyl anion (C3vSiH−3) in the gas phase. The best results in this study agree well with the limited experimental data of Ellison, although new experiments are required for an assessment of our predictions. The theoretical methods employed are the self-consistent field (SCF), configuration interaction with single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD) methods. Basis sets used include double-zeta plus polarization (DZP), triple-zeta plus double polarization (TZ2P), and additional diffuse functions on the silicon atom [DZP+diff(Si), TZ2P+diff(Si)]. The umbrella mode of the silyl anion is most sensitive to basis set quality and electron correlation. Our best predicted vibrational frequency [CISD with TZ2P+diff(Si)] for this particular mode is 890 cm−1. At all levels of theory, the infrared (IR) intensities have been obtained. The planar transition state (D3hSiH−3) has also been studied with respect to its geometry and energy relative to the pyramidal structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459340
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  • 3
    Electronic Resource
    Electronic Resource
    The silyl anion (SiH−3): Cubic/quartic force field and anharmonic contributions to the fundamental vibrational frequencies (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 8112-8121 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fundamental vibrational frequencies for the silyl anion have been determined using two distinct vibrational theoretical methods, namely, the standard second-order perturbation theory and Pulay's variational theory. Several full quartic force fields were determined and used in both vibrational methods. Ab initio quantum mechanical methods used to generate energy derivatives include self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), and coupled cluster with single and double excitations (CCSD), in conjunction with basis sets including double zeta plus polarization (DZP), triple zeta plus double polarization (TZ2P), and TZ2P plus diffuse p functions on the silicon atom [TZ2P+diff(Si)]. SCF energy third derivatives were determined using analytic methods, while SCF fourth derivatives were determined from finite differences of third derivatives. CISD analytic energy gradients were used to generate second, third, and fourth derivatives by finite difference methods. Anharmonic corrections determined from both perturbation and variational theories are found to be quite insensitive to basis set size and electron correlation. The two theoretical methods for the treatment of vibrations have shown small but systematic differences in their prediction of anharmonic corrections. The fundamental vibrational frequencies obtained agree reasonably well with the limited available experimental results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.460094
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  • 4
    Electronic Resource
    Electronic Resource
    Hydrogen bonding between the nitrate anion (conventional and peroxy forms) and the water molecule (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 3379-3388 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio quantum mechanical methods have been applied to the complexes of the nitrate anion (conventional D3h NO−3 and Cs ONOO− forms) with the water molecule, namely, NO−3⋅H2O and ONOO−⋅H2O. Equilibrium geometries and vibrational frequencies for a number of energy minima on the ground state potential energy surface have been determined using analytic energy first and second derivative techniques. The highest level of theory employed is the self-consistent field method with a double-zeta plus polarization basis set. The minimum energy structure (lying ∼15 kcal/mol below separated NO−3 +H2O) incorporates two hydrogen bonds in C2v symmetry. This theoretical dissociation energy agrees well with experiment. A second, more conventional single-hydrogen-bond structure is predicted to lie 2.6 kcal/mol higher in energy. At the most reliable level of theory, no distinct minimum was found for the hydrogen bonded structure between HNO3 (nitric acid) and OH−. Several minima (high lying energetically) between ONOO− and H2O are characterized theoretically.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459692
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  • 5
    Electronic Resource
    Electronic Resource
    The known and unknown group 13 hydride molecules M2H6: Diborane(6), dialane(6), and digallane(6) (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 2868-2876 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular structures, harmonic vibrational frequencies, and infrared intensities for diborane B2H6, dialane Al2H6, and digallane Ga2H6 have been determined using high level ab initio quantum mechanical methods. The highest level of theory employed in this study is the single and double excitation coupled cluster (CCSD) method with double-zeta plus polarization (DZP) basis sets. This study serves to assess the reliabilities of various theoretical methods, laying the foundation for future theoretical studies of larger boron, aluminum, and gallium molecular systems. It appears that the theoretical methods employed here are adequately reliable when compared with existing experiments. Several shortcomings of previous ab initio quantum mechanical studies on diborane(6) and its analogs have been addressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461983
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  • 6
    Electronic Resource
    Electronic Resource
    Finite Td symmetry models for diamond: from adamantane to super-adamantane (C35H36) (1992)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 114 (1992), S. 497-505 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00028a015
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  • 7
    Electronic Resource
    Electronic Resource
    Isomerization of PO3-.(H2O)n clusters to H2PO4-.(H2O)n-1: transition states and barrier heights (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 11169-11179 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00077a015
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  • 8
    Electronic Resource
    Electronic Resource
    [7]Circulene: a remarkably floppy polycyclic aromatic C28H14 isomer (1993)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 3212-3216 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100115a024
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  • 9
    Electronic Resource
    Electronic Resource
    Tungsten hexahydride (WH6). An equilibrium geometry far from octahedral (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 508-521 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio all-electron quantum mechanical methods were applied to the tungsten hexahydride (WH6) molecule using very large basis sets. Seven distinct structures were investigated with full geometry optimizations at the self-consistent field (SCF) level of theory. The effects of electron correlation were estimated with second-order Møller–Plesset perturbation theory (MP2), modified coupled pair functional (MCPF) method, and the coupled cluster with single and double excitations (CCSD) method, and relativistic effects estimated using the Cowan–Griffin (mass–velocity and Darwin) corrections. Our results suggest that the ground state of the tungsten hexahydride (WH6) molecule is a closed-shell triangular prism belonging to the C3v point group, with a set of three hydrogens stacked on top of another set of three hydrogens. From the perspective of inorganic chemistry, it is truly remarkable that the octahedral structure lies 130 kcal/mol above the C3v ground state. Furthermore, these results imply major qualitative differences between WH6 and the well-known W(CH3)6 molecule. Another C3v structure, with one set of three hydrogens staggered with respect to the other set, is energetically nearby. With MCPF and relativistic corrections at the SCF optimized geometry, a third low-lying structure belonging to the C5v point group is virtually degenerate with the triangular prism C3v structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464646
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  • 10
    Electronic Resource
    Electronic Resource
    Aquated metaphosphate (PO3-.cntdot.(H2O)n) clusters. Molecular anion structures, energetics, and vibrational frequencies (1993)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 115 (1993), S. 1943-1951 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00058a047
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