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AbstractAbstract

[en] A perturbative expansion of the electron's Dirac Coulomb propagator around a nonrelativistic form is used to evaluate the one-loop p nonrecoil corrections to ground-state hyperfine splitting in p hydrogenic atoms. A contribution previously estimated as (α/π)(Zα)

^{2}x (18.36 +- 5)E/sub F/ is found to be (α/π) (Zα)^{2}(15.10 +- 0.29)E/sub F/. Theory and experiment are compared for muonium hyperfine splitting and consequences for the fine-structure constant are discussedPrimary Subject

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Journal Article

Journal

Physical Review Letters; ISSN 0031-9007; ; v. 51(11); p. 985-987

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AbstractAbstract

[en] A new model for the ground-state potential energy curves of heteronuclear diatomic molecules is presented. In this model, applicable equally to covalent and ionic bonds, the total potential energy is decomposed into a covalent and an ionic component whose respective contributions are determined by a quantity f, called bond polarity, which is an accurate measure of the ionic character of a bond. The ionic part of the energy is modeled by the Rittner potential, derived using the implicit perturbation theory formalism, while the covalent part is represented by an empirical potential energy function whose parameters are related to atomic constants obtained from the equilibrium spectroscopic properties of the homonuclear diatomic molecules corresponding to the atoms forming the heteronuclear molecule. The new model is applied in detail to the alkali halides. Employing the Hulburt-Hirschfelder potential energy function to represent the covalent component of the energy. Significant improvement in the predicted values of the spectroscopic constants of these molecules is achieved over the earlier models which all consider the alkali halides 100% ionic molecules

Primary Subject

Source

1985; 144 p; University Microfilms Order No. 85-15,904; Thesis (Ph. D.).

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Report

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Thesis/Dissertation

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AbstractAbstract

[en] A suitable extension of the Mori theory to deal with non-hermitian hamiltonians leads to a rigorous justification of models of 'reduced' kind for radiationless decay phenomena. By using the model of an excited state sequentially coupled to two dissipative quasicontinua it is shown that the generalized theory leads to a reduced model consisting of only two 'virtual' states. The standard Mori approach, on the contrary, would result in a chain of more than two states (probably an infinite number of states). It is shown, furthermore, that the biexponential decay behaviour can rigorously be justified in two different ways. The first model only consists of couplings of intramolecular type. The second model also involves an external thermal bath. The generalized Mori theory, when applied to the second model leads to a non phenomenological justification for the kinetic scheme. It is shown, furthermore, that excitations by strong radiation fields result in a different decay behaviour according to whether the former or the latter scheme is applied. (orig.)

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Journal Article

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Advances in Molecular Relaxation and Interaction Processes; ISSN 0378-4487; ; v. 21(2); p. 131-149

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AbstractAbstract

[en] The potential energy surfaces for the X

^{1}A_{1}and first-excited a^{3}B_{2}states of ozone are surveyed with accurate ab initio electronic structure calculations. An efficient technique for using the multiconfiguration self-consistent field (MCSCF) method for polyatomics has been established for these computations, and is described in some detail. The method involves a geometry-dependent flow of configurations between the MCSCF wave function and a small configuration interaction (CI) wave function. The configurations are constructed in a set of 8 core, 7 valence, and 4 ''virtual'' MCSCF orbitals, which are expanded in a double-zeta plus polarization one-electron basis. The vertical and adiabatic excitation energies, uncorrected for zero-point energies, are presently obtained as 1.21 and 0.74 eV, respectively. These results are in agreement with other quantitative theoretical studies which are now available for comparison. Furthermore, the present results indicate that O_{3}(a^{3}B_{2}) has an O_{2}--O binding energy E/sub b/=0.4 eV and that there is no barrier relative to its adiabatic asymptote, O(^{3}P)+O_{2}(X^{3}Σ^{-}/sub g/). These energies are estimated to be accurate to within 0.2 eV. Thus, we conclude that O_{3}(a^{3}B_{2}) is a bound state of ozone. Similar MCSCF/CI calculations are reported for the ring state. The implications of this work for ozone chemistry are discussed. The existence of a second bound state, relative to the ground state atom--diatomic asymptote, may have important consequences with regard to the interpretation and modeling of ozone formation from O(^{3}P) and O_{2}(X^{3}Σ^{-}/sub g/): the a^{3}B_{2}state, as well as the X^{1}A_{1}state, may be involvedPrimary Subject

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Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 74(1); p. 595-607

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AbstractAbstract

[en] The influence of the 5f electron collapse on the energy transitions 5d

^{10}-5d^{9}5f has been investigated in the Hartree-Fock-Pauli approximation for actinides and the elements going before. The energy levels of the configuration 5d^{9}5f were calculated both with the Hartree-Fock functions, depending on the term, as well as with those for the average term. It has been shown that the solution of the Hartree-Fock equations, depending on the term, with the following consideration of the relativistic corrections in the Hartree-Fock- Pauli approximation in the case of the excited atoms with the f- electron collapse, can lead to the change of the order of the energy levels in comparison with that, obtained when the relativistic corrections are not taken into account. The influence of the relativistic corrections has been taken into consideration in the first order of the perturbation theory in the Hartree-Fock-Pauli approximation. The binding energies of 5d electrons have been estimated and compared with the more exact relativistic calculations as well as the experimental data. It has been shown that the value of the relativistic corrections depends considerably on the location of the collapsing nf-electron[ru]

Original Title

Vliyanie kollapsa 5f-ehlektrona na ehnergiyu perekhodov 5d

^{10}-5d^{9}5fPrimary Subject

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Journal Article

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Lietuvos Fizikos Rinkinys; ISSN 0024-2969; ; v. 21(6); p. 66-73

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AbstractAbstract

[en] The counterterm F(epsilon-c) needed for an upper-bound variational principle, to compensate for the additional binding which occurs when a singular repulsion is truncated, is shown to be exponentially small. The proof of this result is based on a coupled-wave expansion of the many-body wave function in products of wave functions for one pair of particles and the A-2 other particles. A simple manipulation of the properties of a second-order linear differential equation in a region of positive potential shows that F(epsilon-c) is of order A(A-1) exp]0.65[V(epsilon-c)]/sup 3/2/ [V'(epsilon-c)]

^{-1}] or less, where V(epsilon-c) is the value at which the singular potential is truncated and V'(epsilon-c) is the corresponding derivative. This result is incorporated in a generalized variational principle which is based on Pade approximants and defines an optimal effective forcePrimary Subject

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AbstractAbstract

[en] The ground-state energy of the two-dimensional (2D) hydrogen molecule has been calculated using a Heitler-London-Rosen-type variational calculation. The value of the dissociation energy is found to be 2.5 Ry. For the interatomic distance R = 0, the variational parameter α/sup 2D/ = 1.7055, corresponding to a 2D He atom. For the sake of comparison, the results of the 3D case are also recalculated. Special interest arises from the Slater integrals, which are rather difficult to obtain in the 2D case

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Ward, M.A.

London Univ. (United Kingdom)

London Univ. (United Kingdom)

AbstractAbstract

No abstract available

Source

Nov 1985; 140 p; Available from British Library Document Supply Centre- DSC:DX198672; Thesis (Ph.D.)

Record Type

Miscellaneous

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Thesis/Dissertation

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AbstractAbstract

[en] MRD--CI calculations were carried out on the potential energy surfaces of the ground and first excited singlet of the same symmetry of H

_{4}, which predict a bound excited state with respect to H_{2}+H(_{2}(B^{1}Σ^{+}/sub u/) of 3.1 eV at a geometry of trigonal pyramid. This geometry was predicted theoretically according to a model of chemical bonding for ''maximum ionicity excited states.'' At the minimum and the three dimensional space surrounding it, there is a near touching of the excited with the ground state hypersurfaces. This fact has implications for the spectroscopy and photochemistry of the H_{2}+H(_{2}systemPrimary Subject

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Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 80(4); p. 1705-1706

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AbstractAbstract

[en] An ab initio multiconfiguration Hartree--Fock (MCHF) study of the X

^{1}Σ^{+}/sub g/, a^{3}Σ^{+}/sub u/, B^{1}Δ/sub u/, and C^{1}Pi/sub u/ states of cyanogen (C_{2}N_{2}) is presented. Equilibrium structures, harmonic vibrational frequencies, excitation energies, and dissociation energies have been calculated and found to be in semiquantitative agreement with available experimental data. This study confirms the π → π* character of C_{2}N_{2}(a^{3}Σ^{+}/sub u/) and C_{2}N_{2}(B^{1}Δ/sub u/), and the n → π* character of C_{2}N_{2}(C^{1}Pi/sub u/) near their equilibrium structures. Configuration mixing among the n and π electrons is needed to correct the broken symmetry description given by the Hartree--Fock (HF) method, and leads to a qualitatively correct representation of these states. For C_{2}N_{2}(a^{3}Σ^{+}/sub u/) and C_{2}N_{2}(B^{1}Δ/sub u/), the harmonic force constants show a strong through-bond interaction which is due to the dominance of the charge transfer configuration^{+}NCCN^{-}Primary Subject

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Journal Article

Journal

Journal of Chemical Physics; ISSN 0021-9606; ; v. 83(1); p. 265-272

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