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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio configuration interaction study of mixed BeLik clusters (k=1–9) (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 5794-5802 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electronic and geometric structure of mixed neutral BeLik and cationic BeLi+k clusters (k=1–9) has been investigated employing ab initio configuration interaction quantum chemical methods. The values of atomization energies per atom for BeLik with k〈7 and for BeLi+k with k〈8 increase strongly with the cluster size. The binding energy per atom remains nearly unchanged for neutral BeLik with k=7–9 and cationic BeLi+k clusters with k=8 and 9. The quantities which measure cluster stability towards fragmentation processes predict high stabilities for BeLi6 and BeLi+7. The geometries of cluster, their stabilities as well as other properties can be easily interpreted as simple consequences of the nodal properties of the cluster MOs. The connection between the results obtained from this work and from the superatom model has been pointed out. The specific nature of the chemical bonding in mixed clusters obtained from quantum chemical investigations has been analyzed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455555
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  • 2
    Electronic Resource
    Electronic Resource
    Ab initio configuration interaction study of the electronic and geometric structures of small sodium cationic clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 4861-4866 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The favorable geometries of small sodium clusters Na+n (n=3–9) are determined with the analytical gradient method in the framework of the ab initio SCF approximation. The transition from the planar towards three-dimensional cluster geometries is understood in terms of some basic quantum theoretical concepts. The binding energies per atom for Na+n clusters calculated with the MRD CI procedure increase, in general, as a function of n. Nevertheless, the atomization energy per atom as well as the ionization potential as functions of the nuclearity n exhibit well developed oscillations for even–odd n. Consequently, the fragmentation energy for the channel Na+n→Na+n−1+Na shows strong oscillations as well. This explains large abundances of cationic clusters with odd nuclearity found in some detection devices. The possible consequences for the fragmentation process of Na+n is discussed. It is found that the process Na+n→Na+n−2+Na2 is favorable for Na+5, Na+7, and Na+9.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455681
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic states of cyclobutadiene heteroanalogs. Critical biradicaloids (1989)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 111 (1989), S. 6140-6146 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00198a024
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  • 4
    Electronic Resource
    Electronic Resource
    The quenching of Na*(3p) in collisions with N2: A classical trajectory study (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 86 (1987), S. 822-836 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The quenching reaction Na(2P)+N2(1Σ+g,v,J)→Na(2S) +N2(1Σ+g,v',J') has been studied. Scattering calculations have been performed using the surface hopping trajectory method for the two energetically lowest potential energy surfaces of NaN2. The latter have been determined in an ab initio MRD-CI treatment. They exhibit a (avoided) crossing where quenching is likely to occur. Model potentials, which are constructed along the lines given by the ab initio surfaces, are used to investigate the influence of the shape of the potential on the scattering process. Cross sections and final translational energy distributions are compared with experimental data. Alignment and orientation as expressed by the collision induced density matrix have also been considered. Theoretical and experimental results show good agreement. The detailed analysis of the scattering calculations have provided with a better understanding of the quenching process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452761
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  • 5
    Electronic Resource
    Electronic Resource
    Charge-transfer-biradical excited states: relation to anomalous fluorescence. "Negative" S1-T1 splitting in twisted aminoborane (1985)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 107 (1985), S. 1765-1766 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00292a055
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  • 6
    Electronic Resource
    Electronic Resource
    Photochemicalsyn-anti isomerization of a Schiff base: A two-dimensional description of a conical intersection in formaldimine (1985)
    Springer
    Theoretical chemistry accounts 68 (1985), S. 45-55 
    Details
    ISSN: 1432-2234
    Keywords: Photochemistry ; syn-anti isomerization ; Formaldimine ; Conical intersection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The shape of theS 0,S 1, andT 1 potential energy surfaces of formaldimine, CH2=NH, is explored in the two-dimensional subspace defined by the twisting and linear inversion motions which correspond to the geometricalsyn-anti isomerization, using anab initio large-scale CI method. Minima in theS 1 andT 1 surfaces as well as aS 0-S 1 conical intersection are identified and the photoisomerization mechanism is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00698750
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  • 7
    Electronic Resource
    Electronic Resource
    The pseudopotential-CI study of the interaction between ethylene and metal atoms, metal Oxides, and their cations (Me = Be, Mg, and Zn) (1986)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 29 (1986), S. 1535-1554 
    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: Potential energy curves for the lowest singlet and triplet states of Me + C2H4, Me+ + C2H4, MeO, MeO + C2H4, and (MeO + C2H4)+ systems for Me = Be, Mg, and Zn have been determined employing PP-MRD-CI or an all electron MRD-CI procedure. A binding interaction in the ground state has been found for oxides, all cation systems, and the BeO + C2H4 system. In the cases of MgO + C2H4 and ZnO + C2H4, only low lying excited states exhibit attractive interactions. Among three oxides considered, BeO is less pronounced biradically than MgO and ZnO. In order to obtain a binding interaction between an oxide and the olefin in the ground state, the p orbital of the metal must be sufficiently involved in binding.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560290544
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  • 8
    Electronic Resource
    Electronic Resource
    Neutrale und geladene Diradikale, Zwitterionen, Trichter auf der S1-Hyperfläche und Protonentranslokation; ihre Bedeutung für den Sehvorgang und andere photochemische und photophysikalische Prozesse (1987)
    Weinheim : Wiley-Blackwell
    Zeitschrift für die chemische Industrie 99 (1987), S. 216-236 
    Details
    ISSN: 0044-8249
    Keywords: Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Um die Struktur von Photoprodukten verstehen zu können, ist es wesentlich, diejenigen Geometrien zu kennen, bei denen Moleküle aus angeregten Zuständen in den Grundzustand (S0) zurückkehren. In Frage kommen dabei vor allem Geometrien, die lokalen Minima auf den Potentialhyperflächen der S1- (energieärmstes angeregtes Singulett) oder T1-Zustände (energieärmstes Triplett) oder konischen Durchschneidungen („Trichter“, „Funnels“) der Hyperflächen der S0- und S1-Zustände entsprechen. Obwohl für ausreichend kleine Moleküle derartige Geometrien heute bereits, wenn auch mit großem Aufwand, numerisch bestimmt werden können, wären qualitativere, damit aber zugleich allgemeinere Aussagen über diejenigen Geometrien photochemischer Systeme, bei denen sich die Hyperflächen der S0- und S1-Zustände nähern, von Interesse. Viele dieser Geometrien sind mit einem diradikaloiden Charakter des Systems verknüpft, so daß es sinnvoll ist, die Eigenschaften von Diradikalen und verwandten Spezies eingehender zu untersuchen. Nach einem Überblick über das Zweielektronen-Zweiorbitale-Modell für Moleküle mit Diradikaloid-Geometrien werden die Bedingungen für eine Berührung von S0- und S1-Hyperflächen formuliert. Gestützt werden die Ergebnisse des einfachen Modells durch die umfangreicher ab-initio-Konfigurationswechselwirkungs(CI)rechnungen für die Verdrillung von Ethylen im polarisierenden Feld einer positiven Ladung, für die Verdrillung um geladene Doppel-bindungen und um Einfachbindungen zwischen π-Donor und π-Acceptor, sowie durch die Ergebnisse ähnlicher Rechnungen für „push-pull“-substituierte Cyclobutadiene. In einigen Fällen werden nahezu entartete S0-, S1- und T1-Zustände vorhergesagt. Die naheliegenden Konsequenzen, die aus diesen Befunden für die mechanistische Beschreibung der cis-trans-Isomerisierung, der Bildung von TICT-Zuständen (Twisted Intramolecular Charge Transfer), der Protonentranslokation und - möglicherweise - des ersten Schritts beim Sehvorgang zu ziehen sind, werden zusammengefaßt. Darüber hinaus sind die Ergebnisse wichtig für das Verständnis der Regiospezifität von Singulett-Photocycloadditionen.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/ange.19870990308
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  • 9
    Electronic Resource
    Electronic Resource
    Neutral and Charged Biradicals, Zwitterions, Funnels in S1, and Proton Translocation: Their Role in Photochemistry, Photophysics, and Vision (1987)
    Weinheim : Wiley-Blackwell
    Angewandte Chemie International Edition in English 26 (1987), S. 170-189 
    Details
    ISSN: 0570-0833
    Keywords: Free radicals ; Zwitterions ; Diradicals ; Quantum chemistry ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A knowledge of the geometries at which excited molecules return to the electronic ground state (S0) is essential for the understanding of the structures of photoproducts. Particularly good candidates are geometries corresponding to local minima on the S1 (lowest excited singlet) and T1(lowest triplet) surfaces, as well as S0-S1 conical intersections (funnels). Given sufficient effort, such geometries can nowadays be found numerically for small enough molecules. Still, it is interesting to ask whether more approximate, but also more general, statements can be made concerning the geometries at which the S0 and S1 surfaces closely approach each other. Since many of these are biradicaloid geometries, it is logical to examine the properties of biradicals and related species at some length. After reviewing the two-electron two-orbital model for molecules at biradicaloid geometries, we formulate the conditions under which the S0 and S1 surfaces touch. The results obtained for the simple model are supported by ab initio large-scale configuration interaction (CI) calculations for the twisting of ethylene in the polarizing field of a positive charge and for the twisting of charged double bonds and π-donor-to-π-acceptor single bonds, and by similar calculations for “push-pull” perturbed cyclobutadienes, some of which are predicted to have nearly degenerate S0, S1, and T1 states. The likely consequences of these results for the detailed description of the mechanisms of cis-trans isomerization, the formation of twisted internal charge-transfer (TICT) states, proton translocation, and possibly of the initial step in vision, as well as for the understanding of the regiospecificity of singlet photocycloaddition, are summarized.
    Additional Material: 16 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/anie.198701701
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