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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 1176-1186 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Large ab initio calculations on the low-lying 2Δ, 2Π, and 2Σ+ electronic states of NiH have been performed employing a relativistically corrected Hamiltonian. The relative ordering of the unperturbed electronic states is found to be 2Δ〈2Σ+〈2Π. Diagonal and off-diagonal spin–orbit matrix elements have been evaluated within the Breit–Pauli approximation and were used to couple the individual vibronic functions. With the exception of 〈2Σ+1/2||HSO||2Π1/2〉, the spin–orbit matrix elements are found to be nearly independent of the internuclear distance. Their magnitude is determined by coupling matrix elements of the components of a pure atomic d9 configuration. The deflection of the 〈2Σ+1/2||HSO||2Π1/2〉 matrix element from the d9 limit at shorter bond distances can be attributed to increased admixture of d10 character in the 2Σ+ wave function. For NiH the v=0, J=2.5 level of the 2Δ3/2 state is calculated at 1014 cm−1, in excellent agreement with experiments (1012 cm−1). The lower of the heavily mixed 2Σ+1/2 and 2Π1/2 combinations with total angular momentum J=2.5 is located at 2279 cm−1, approximately 150 cm−1 above the corresponding experimental value. Shifting the 2Σ+ potential curve by −250 cm−1 brings the calculated levels of the Ω=1/2 system into almost perfect agreement with observed levels averaged over e and f components. The upper, experimentally not yet determined component is predicted at approximately 3655 cm−1, close to the v=2 level of the 2Δ5/2 state. The 2Π3/2 v=0, J=2.5 and the 2Δ3/2 v=1, J=2.5 levels, located at 2631 and 3091 cm−1, are considerably mixed. Excitation energies to several higher-lying vibronic states of NiH and a corresponding analysis of the vibronic spectrum of the NiD isotope are also reported.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 6086-6099 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy surfaces for the electronic states of the HCCS radical correlating at linear nuclear arrangement with the X 2Π state are calculated by means of an extensive ab initio approach. Particular attention is paid to calculating accurate three-dimensional potential surfaces involving variations of two bending and torsional coordinates, which play the central role in vibronic interactions (Renner–Teller effect), determining the structure of spectra of this radical. In the second part of this paper we use these potential surfaces and the ab initio computed spin–orbit coupling constant to calculate vibronic spectra of HCCS and DCCS in the framework of a theoretical model developed in our laboratory. The results of the present study are in excellent agreement with those derived by Tang and Saito [J. Chem. Phys. 105, 8020 (1996)] and thus strongly support the interpretation of their experimental findings. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 5574-5585 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic states of CuH correlating with the two lowest dissociation channels have been studied by ab initio methods. Potential energy curves, electric dipole (transition) moments, and spin–orbit coupling matrix elements are evaluated using correlated wave functions determined from the (relativistic) no-pair equation. The excited states of CuH and CuD cannot be characterized as pure spin states. By including spin–orbit coupling in the calculations, a one to one correspondence can be established between experimentally known term energies and computed level positions. The A 1Σ+ and B 3Π0+ states results from different linear combinations of 1 1Σ+ and 1 3Π0+. The 3Π state is found to have an inverted fine-structure pattern in contradiction to earlier assumptions. The experimentally known C1 and c1 states originate from admixtures of 1 3Δ and 1 1Π. The large coupling between LS states explains the intensity of the otherwise forbidden transitions from 3Π and 3Δ to the ground state. Among the states predicted from the present analysis is a low-lying 3Σ+ state which may be responsible for the bands observed in the red region.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Theoretical chemistry accounts 81 (1992), S. 375-390 
    ISSN: 1432-2234
    Keywords: Copper ; Excited electronic states ; Relativistic wavefunctions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The2 S g (d 10 s 1),2 D g (d 9 s 2),2 P u (d 10 p 1),2,4{F,P} u (d 9 s 1 p 1) states of copper as well as the1 S g (d 10) state of the positive copper ion are studied byab initio methods. Relativistic wavefunctions are determined variationally solving a one-component no-pair equation. This approximation makes it possible to treat all the states in a common set of orbitals. It is found that differential relativistic effects for the excitation energies are independent of the one-particle basis employed. The first-order perturbation estimate using the mass-velocity and Darwin operators depends critically on the description of the 3s and 3p core electrons. Among the various one-particle sets tested,2 D g orbitals, with the (4s, 4p) near-degeneracy effects included in the orbital optimization step, are most appropriate for the correlation treatment. They give an error of 0.3 eV for the2 S g –2 D g separation only slightly inferior to our best result employing parent orbitals for both states. All other states agree with experiment to within 0.2 eV. The first-order spin-orbit splitting of the2 D g state (−2006 cm−1) is in excellent agreement with the experimental value.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1434-6079
    Keywords: 31.25.Qm ; 33.15.Mt ; 82.20.Kh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A two-dimensional symmetric stretching-bending potential surface for the electronic ground state of the XeF2 molecule has been computed by means of self-consistent field and multi-reference configuration interaction methods. At the correlated level of treatment it is found that the linear nuclear arrangement of XeF2 with XeF bond distances close to 200 pm corresponds only to a local minimum on the potential energy surface separated from the dissociation products Xe + 2F by a high energy barrier. The results of a vibrational analysis study enable a reliable reproduction and interpretation of available experimental data concerning the infrared spectrum of the molecule.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Zeitschrift für anorganische Chemie 621 (1995), S. 2065-2069 
    ISSN: 0044-2313
    Keywords: Tetraphosphorus hexaoxide monoselenide ; preparation ; crystal structure ; Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Synthesis, Crystal Structure, and Spectroscopic Characterization of Tetraphosphorus Hexaoxide Monoselenide, P4O6SeP4O6Se has been synthesized by photochemical reaction between P4O6 and elemental selenium in CS2 in presence of iodine as a catalyst. Single crystals form at purification via sublimation. The compound (m. p. 46°C) crystallizes in the monoclinic space group P21/c (no. 14) with a = 1 051.8(2), b = 652.9(1), c = 1 178.6(2) pm, β = 109.29(1)°, Z = 4. Within the limits of experimental error, the molecules exhibit C3v symmetry. IR, Raman, and 31P n.m.r. (solution) spectra of the compound are reported and discussed. The geometry of the Molecule as determined by theoretical methods (SCF level) is in good agreement with the experimental results.
    Notes: P4O6Se wurde durch photochemische Reaktion von P4O6 mit elementarem Selen in CS2 in Gegenwart von Iod als Katalysator dargestellt; Einkristalle entstanden bei der Reinigung durch Sublimation. Die Verbindung (Fp. 46°C) kristallisiert in der monoklinen Raumgruppe P21/c (Nr. 14) mit a = 1 051,8(2), b = 652,9(1), c = 1 178,6(2) pm, β = 109,29(1)°, Z = 4. Im Rahmen der Fehlergrenzen der Strukturbestimmung besitzen die Moleküle C3v-Symmetrie. IR-, Raman- und 31P-Lösungs-NMR-Spektren der Verbindung werden mitgeteilt und diskutiert. Die mit quantenchemischen Methoden auf SCF-Niveau berechnete Molekülgeometrie stimmt mit der experimentell bestimmten gut überein.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 43 (1992), S. 659-668 
    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: The definition of so-called first-order properties is, in general, not unique for approximate solutions of the Schrödinger equation. In the present work, the determination of molecular properties as the expectation value or energy derivative are compared for a wide class of electron correlation treatments that are based on the stationarity of certain modified energy functionals. The case in which all perturbation-dependent parameters in the energy expression are optimized is taken as a reference point, to which the derivative and the expectation value approaches are related by a sequence of approximations. By analyzing the validity of these approximations, we are in a position to give general criteria for the choice of the method to be employed. The derivative approach is shown to be a special case of a general method to improve the calculation of molecular properties. Furthermore, this method is extended to give a correction to the energy itself. © 1992 John Wiley & Sons, Inc.
    Type of Medium: Electronic Resource
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