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  • 1990-1994  (6)
  • 1965-1969  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 87 (1994), S. 343-371 
    ISSN: 1432-2234
    Keywords: Benzene ; Phosphorescence ; Decay
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary Radiative decay and phosphorescence of triplet stare benzene is doubly -orbital and spin- forbidden and is only activated through vibronic coupling among the manifold of triplet states. For this reason the determination of lifetime and transition moments for the decay of triplet benzene has posed a considerable challenge to both theory and experiment. In the present work we have addressed the triplet benzene problem at several levels of theory; by truncated perturbation theory and semiempirical, CNDO/S-CI, calculations; by complete sum-over-state calculations as implemented in recentab initio multiconfiguration quadratic response (MCQR) theory; and by direct MCQR calculations of vibronic phosphorescence. The vibronic coupling is in the two former cases treated by the Herzberg-Teller (H-T) perturbation theory, involving four main mechanisms for the phosphorescent decay of triplet benzene. The results and interpretations given by these approaches as well as their merits and limitations are presented and discussed in some detail. Our calculations indicate that the phosphorescent decay of the3 B 1u state takes place predominantly through vibronic coupling along thee 2g mode. We obtain a phosphorescence that is almost completely out-of-plane polarized, which is in line with more recent measurements by the microwave-induced delayed phosphorescence technique, and could reproduce quite well the intensity ratios for different vibronic bands obtained in that experiment. The final triplet state lifetime is the result of a delicate sum of contributions from several vibronic degenerate and non-degenerate modes. The direct vibronic phosphorescence calculations predict a long lifetime, about one minute — 68 seconds for the best wavefunction — and seem to focus on a doubling of the assumed, albeit not established, “best experimental” value for the radiative lifetime of triplet benzene; ⋍ 30 seconds.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-8647
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Russian physics journal 12 (1969), S. 1260-1263 
    ISSN: 1573-9228
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and experimental chemistry 27 (1991), S. 582-586 
    ISSN: 1573-935X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The chemical ionization mechanism for HCO 2 + is considered from MINDO/3 CI calculations and ones on the spin-orbit interaction elements, which has been employed in examining the sections of the potential-energy surfaces along the reaction coordinates in the formation of HCO 2 + and HCO 2 + .
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 38 (1990), S. 779-797 
    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: A new constructive approach for deriving a quantum field chemistry (QFC) is proposed. As a matter of fact, the approach is a direct application of the concept of spontaneously broken symmetry of a free-electron-field vacuum to the exact definition of a condensed-state chemical microstructure. The main idea is to identify the properly modified ground states of the vacuum with ground states of some compact quasi-molecular systems condensed in a set of “kink”-bounded molecular {vα} subspaces. Phase transitions of the electron vacuum are as usually expressed in terms of quantum order parameter set {φα1(x) = [ρα1(x)]1/2 exp(iλα)}, which defines a single electron densities ρα1(x)=nα(x)/Nα (here Nα=∫nα(x) dx) in exact molecule ground states ρα1(x)=|α1(x)|2. The order parameters are obtained by the self-consistent procedure of minimizing the ground-state energy Eα=Nα∊α-1(N) for each open molecular “compacton” with respect to the number of electrons Nα and an average single-electron energy ∊α-1(Nα). Account is taken of topological definitions of the various molecular constituents: atoms, atomic functional groups, molecules, and their clusters. The stability of diverse clusters is investigated by the method of approximating quasi-particle density functional (AQDF). It gives particular attention to the description of peculiar intermolecular clusters (Mn) composed with single-atom molecules (M1=A). Such clusters may be used to simulate some active centers that bear the responsibility for strong effects of nonlinearity and dissipation in condensed states. Some results of AQDF-calculation of small active Rh-clusters (n=2, 3, 4) are taken under consideration to illustrate that such clusters resemble neither fragments of bulk solids nor molecules in a gas.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-935X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Calculations have been performed in the orbital-shell density-functional approximation from the nonempirical approximating quasiparticle density function, which show that the total potential energy surface for the CrBz complex is described by a two-well interaction potential. The minimum in the short-range part of the potential corresponds to an intramolecular bond in a bisarenechromium charge-transfer complex, while the minimum in the long-range part describes the molecular interaction between those components in atomically dispersed solutions of chromium in arene matrices. Good agreement with experiment is obtained.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical and experimental chemistry 25 (1990), S. 441-445 
    ISSN: 1573-935X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A system modelling the photochemical abstraction of a hydrogen atom by ketones in alcohols is calculated by the semiempirical INDO and MINDO/3 methods with allowance for the configuration interaction in the singly and doubly excited states. The states participating in the elimination reaction and the electronic rearrangement taking place in the course of the reaction are traced on the basis of an analysis of the wave functions and the electron and spin densities. It is established that the state of the ketone which participates in hydrogen abstraction is a lowest triplet state of the nπ* type, which is formed through the avoidance of intersections of several states of different orbital type 3π*, 3nσ* and the charge-transfer state.
    Type of Medium: Electronic Resource
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