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  • 1
    Electronic Resource
    Electronic Resource
    On the evaluation of lifetimes for spin-forbidden radiative transitions originating in coupling to states embedded in a continuum. Application to CH− (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3853-3860 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A recently developed method for treating spin-forbidden electronic transitions within the Breit–Pauli approximation is shown to provide a means for characterizing such processes when the transitions derive their intensity by coupling to states embedded in a continuum. The success of this approach is attributable principally to the need to specify only the configuration state function space, rather than its spectrum relative to Hˆ0, in order to obtain the first order perturbation contribution (Ψ1I) to the wave function. Here Hˆ0 is the nonrelativistic Born–Oppenheimer Hamiltonian and Ψ1I is the solution of (Hˆ0−E0I) Ψ1I=−HˆsoΨ0I where Hˆso is the full microscopic spin–orbit portion of the Breit–Pauli interaction. A method for improving the molecular orbital basis used to describe Ψ1I based on the iterative natural orbital (INO) procedure is introduced. The a 1Δ→X 3Σ− transition in CH− was considered. Using the INO procedure, it was found that the optimum orbital space for describing Ψ1I includes a molecular orbital with character intermediate between the compact valence orbital and the diffuse orbital obtained from two alternative MCSCF procedures. Equivalent INO orbitals were obtained from these two distinctly different starting points. Using the INO orbital set, a total radiative rate for the ground vibrational level of the a 1Δ state of 0.163 s−1 was obtained which gives a lifetime, τ=6.14(±1.2) s. This value is in excellent agreement with the experimental value τ=5.9(+0.8, −0.6) s reported by Okumura et al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453887
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  • 2
    Electronic Resource
    Electronic Resource
    The electronic and vibrational energies of two double-welled 3Σ+u states of He2 (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 4000-4007 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The potential energy curves for the 3Σ+u states of He2 which correspond to the interactions of He 1s2 1S with He 1s2s 3S and He 1s2s 3S with He 1s2s 3S are obtained from second-order configuration interaction calculations which themselves are based on a multiconfiguration self-consistent field calculation. The basis set includes functions obtained by optimizing the dipole, quadrupole, and octapole polarizability of the 3S atom and the dipole and quadrupole polarizabilities of the ground 1S atom. For the lowest 3Σ+u state we estimate the dissociation energy to be De =15 740±60 cm−1; we agree to within about 4 cm−1 with the observed vibrational energy level differences, and agree nicely with the position and depth of the short-range minimum deduced from spectra. We also obtain a potential hump at intermediate separations whose main features agree very well with those obtained from scattering experiments. The potential curve exhibits a van der Waals minimum about 3.82 cm−1 deep at about 11.6 a0. The excited 3Σ+u state has a deep metastable well at small internuclear separations as well as a well in the intermediate region which is about 3430 cm−1 deep.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.452903
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  • 3
    Electronic Resource
    Electronic Resource
    Theoretical study of the radiative lifetime for the spin-forbidden transition a 3Σ+u→X 1Σ+g in He2 (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 2504-2512 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The radiative lifetime for the spin-forbidden, dipole-allowed transition a3Σ+u→X1Σ+g in neutral He2 was calculated. This transition is assumed to derive its intensity by spin–orbit (SO) induced couplings which are treated using first-order perturbation theory. The first-order corrections to the wave functions are calculated directly in the configuration state function (CSF) basis by solving a system of linear equations given by first-order perturbation theory for the perturbation to the zeroth-order X1Σ+g and a3Σ+u wave functions. This approach eliminates the need to solve explicitly for many eigenstates of the unperturbed Hamiltonian which would be required if the spectral representation for the perturbed wave function were used. The results show a rapidly changing electric transition dipole moment as a function of internuclear seperation, R(He–He), over the bound region of the a3Σ+u potential energy curve, i.e., R(He–He)=1.5 to 4.0 bohr. The transition dipole reaches a maximum near the small barrier to dissociation around R(He–He)=4.5 bohr. A vibrational analysis gives the lifetime of the v=0 level of a3Σ+u to be approximately 18 s, which is consistent with a recent experimental estimate of 10 s (v=?) as a lower bound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455993
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  • 4
    Electronic Resource
    Electronic Resource
    The lower electronic states of ClOO: A computational investigation (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1693-1701 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Eight doublet and eight quartet states of ClOO were investigated by ab initio CI techniques. The potential energy surfaces of the four lowest energy doublet states of both A″ and A′ symmetry indicate that only the 1 2A″ state is bound. In contrast to the model provided by the HO2 radical, all of the excited doublet states investigated were repulsive with respect to dissociation to Cl+O2 and metastable or bound with respect to dissociation to ClO+O. The transitions to the excited states investigated span the visible and near UV spectral regions, but the transition moments indicate that they are very weak. Since the photolysis products are the same as those of the rapid thermal dissociation, photolysis is not expected to be an important atmospheric process. The soft bending potential for the 1 2A′ state and the shape of the 1 4A″ state in the entrance channel of the ClO+O → Cl+O2 reaction provide a qualitative explanation for the underprediction of the low temperature reaction rate by previous trajectory calculations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449356
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  • 5
    Electronic Resource
    Electronic Resource
    On the evaluation of nonadiabatic coupling matrix elements for MCSCF/CI wave functions using analytic derivative methods. III. Second derivative terms (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 348-353 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A method for the efficient evaluation of nonadiabatic coupling matrix elements of the form 〈Ψ J(r;R)||(∂2/∂R2α) Ψ I(r;R)〉r is presented. The electronic wave functions Ψ J and Ψ I are assumed to be MCSCF/CI wave functions whose common molecular orbital basis is determined within the state averaged MCSCF (SA-MCSCF) approximation. The method derives its efficiency by exploiting analogies with analytic CI second derivative techniques and from the first and second derivative coupled perturbed SA-MCSCF equations. This method is compared with an existing finite difference procedure which is reformulated to take maximal advantage of analytic gradient methods.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450144
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  • 6
    Electronic Resource
    Electronic Resource
    Open-shell ground state wave functions for linear polyacenes (1978)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 82 (1978), S. 1436-1438 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100501a022
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  • 7
    Electronic Resource
    Electronic Resource
    Calculation of molecular electronic spectra by projected-unrestricted Hartree-Fock theory (1977)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 11 (1977), S. 591-604 
    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: This paper is concerned with a new application of projected-unrestricted Hartree-Fock theory, namely, the calculation of electronic spectra for symmetric molecules. The excited electronic state is represented by a single determinant whose unrestricted nature allows for orbital rearrangement relative to the self-consistent ground state. The self-consistent calculation must be followed by spin projection to obtain appropriate spin eigenstates. It was necessary to develop modified procedures for portions of the spin projection calculation because our method of constructing the wave functions produces degeneracies among the natural orbitals. Illustrative calculations using the all-valence-electron INDO approximations produced results which compared favorably with configuration-interaction treatments. The method described here should be most useful, however, in conjunction with ab initio calculations using flexible basis sets.
    Additional Material: 4 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560110406
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  • 8
    Electronic Resource
    Electronic Resource
    Improved CI formula evaluation: Elimination of the phase determination at the determinant level for arbitrarily coupled CSFs (1981)
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 649-654 
    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: The amount of work needed to evaluate the matrix elements in a configuration interaction calculation can be very large. This is especially true if the phase associated with bringing determinants into maximum coincidence is evaluated at the determinant level. A method is presented which allows the phase to be determined at the occupation level for arbitrarily coupled configuration state functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/qua.560190416
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  • 9
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    Open-shell ground state wave functions for linear polyacenes (1978)
    American Chemical Society
    Details
    Publication Date: 1978-06-01
    Print ISSN: 0022-3654
    Electronic ISSN: 1541-5740
    Topics: Chemistry and Pharmacology , Physics
    Published by American Chemical Society
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  • 10
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    On the evaluation of nonadiabatic coupling matrix elements using SA‐MCSCF/CI wave functions and analytic gradient methods. I (1984)
    American Institute of Physics
    Details
    Publication Date: 1984-11-15
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics
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