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  • 1
    Electronic Resource
    Electronic Resource
    Ab initio calculations of the vibronically averaged hyperfine coupling constants for the 1 2Πu electronic state of CH2+ (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 7629-7636 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The results of pure ab initio calculations of the hyperfine coupling constants for the 1 2Πu electronic state for various isotopomers of CH2+ in the energy range between 0 and 20 000 cm−1 are presented. Effects of vibronic and spin–orbit coupling are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463483
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  • 2
    Electronic Resource
    Electronic Resource
    Study of the hyperfine coupling constants (14N and 1H) of the NH2 molecules in the X 2B1 ground state and the A 2A1 excited state (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4526-4535 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperfine coupling constants (hfcc) Aiso and Aij are calculated for the atoms of NH2 in its two lowest-lying electronic states at various molecular geometries by means of the ab initio multireference configuration interaction method. The vibronically averaged values of the hfccs for the K=0 and 1 levels in 14N 1H2 in the energy range up to 20 000 cm−1 are computed. Polarization effects which determine Aiso as well as a simple model to describe the dipolar hfccs are discussed. All results are in excellent agreement with experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462814
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  • 3
    Electronic Resource
    Electronic Resource
    Ab initio calculation of the vibronically averaged values for the hyperfine coupling constants in NH2, NHD, and ND2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 4996-5006 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Vibronically averaged values for K=0 and K=1 bending levels in the energy range between 0 and 25 000 cm−1 are computed for the 14N, H, and D atoms in NH2, NHD, and ND2. The pure ab initio electronic potentials, as well as those derived by fitting of experimentally observed band positions are employed. Effects of vibronic coupling and local perturbations of close-lying levels belonging to different electronic states are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463853
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  • 4
    Electronic Resource
    Electronic Resource
    Multireference Configuration Interaction and Density Functional Study of the Azetidine Radical Cation and the Neutral Azetidin-1-yl Radical (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 9724-9729 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100024a013
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  • 5
    Electronic Resource
    Electronic Resource
    A multireference configuration interaction study of the hyperfine structure of the molecules CCO, CNN, and NCN in their triplet ground states (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 7686-7691 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperfine structures of the isoelectronic molecules CCO, CNN, and NCN in their triplet ground states (X 3Σ−) are investigated by means of ab initio methods. The infrared frequencies and geometries are determined and compared with experiment. Configuration selected multireference configuration interaction calculations in combination with perturbation theory to correct the wave function (MRD-CI/BK) employing extended atomic orbital (AO) basis sets yielded very accurate hyperfine properties. The theoretical values for CCO are in excellent agreement with the experimental values determined by Smith and Weltner [J. Chem. Phys. 62, 4592 (1975)]. For CNN, the first assignment of Smith and Weltner for the two nitrogen atoms has to be changed. A qualitative discussion of the electronic structure discloses no simple relation between the structure of the singly occupied orbitals and the measured hyperfine coupling constants. Vibrational effects were found to be of little importance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468262
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  • 6
    Electronic Resource
    Electronic Resource
    Ab initio study of the energy difference between the cyclic and linear forms of the C6 molecule (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 4042-4048 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The energy difference between the three lowest-lying isomers of C6, the linear 3Σ−g state, and the two ring forms, the benzene structure (1A1g) possessing D6h symmetry and a distorted cyclic form (1A1', D3h symmetry) have been calculated using various ab initio methods. Variational methods such as multireference configuration interaction (MR-CI) and complete active space second order perturbation treatment (CASPT2) have been applied, as well as perturbational treatments and coupled cluster calculations (CCD). The correlation of all valence shell electrons is found to be important for a balanced description of the isomers of C6. Methods which do not account for higher-order effects appropriately proved to be unsuitable for calculating the energy difference correctly. The results from multireference configuration interaction methods show that the isomers are close in energy with the cyclic forms somewhat lower than the linear form. The ring form possessing D3h symmetry (1A1') is found to be the lowest-lying structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.467521
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical study of electron spin resonance parameters: H2CN and H2CO+ (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2936-2942 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The hyperfine structure of the two isoelectronic molecules H2CN and H2CO+ in their electronic ground state (X 2B2) is studied. The influence of the atomic orbital (AO) basis sets, of the correlation treatment, and of the equilibrium geometry on the obtained hyperfine properties is investigated. It is found that the multireference double excitation-configuration interaction (MRD-CI)/BK treatment in which an MRD-CI wave function is corrected by a modified BK method yields equivalent results to quadratic CI [QCISD(T)], coupled cluster single doubles [CCSD(T)], or Brueckner doubles [BD(T)]. Uncertainties in the equilibrium geometries are found to be the major source for discrepancies between theoretically and experimentally determined isotropic hyperfine coupling constants (hfccs). For the heavier centers, the calculated values of the isotropic hfccs agrees nearly perfectly with experimental values (≈1%–2%). The calculated values for the hydrogens are too low, but using the equilibrium structure suggested by Yamamoto and Sato [J. Chem. Phys. 96, 4157 (1992)], the best estimate deviates by less than 3%.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466435
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  • 8
    Electronic Resource
    Electronic Resource
    A detailed study of the configuration selected multireference configuration interaction method combined with perturbation theory to correct the wave function (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1380-1386 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A reliable prediction of the isotropic hyperfine coupling constant Aiso is still a difficult task for ab initio calculations. In previous studies, the configuration selected multireference configuration interaction method in combination with perturbation theory to correct the wave function (MRCI/BK) yielded accurate isotropic hyperfine coupling constants very economically. The present study gives a detailed analysis of the MRCI/BK method based on the X 2Π state of CH as a test case. Furthermore, a comparison to various other methods such as Møller–Plesset perturbation theory and the coupled cluster approach is made. The success of the MRCI/BK method in predicting isotropic hyperfine coupling constants is explained in terms of the influence of higher than double excitations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466616
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  • 9
    Electronic Resource
    Electronic Resource
    Theoretical Study of the Reaction O(3P) + C2H4 and Comparison with the 3CH2 + C2H4 Reaction (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 9541-9545 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100089a029
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  • 10
    Electronic Resource
    Electronic Resource
    On a theoretical model for the Renner–Teller effect in tetra-atomic molecules (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 8569-8585 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model for the ab initio treatment of the Renner–Teller effect in tetra-atomic molecules is elaborated. It is based on the approach developed by Petelin and Kiselev [Int. J. Quantum Chem. 6, 701 (1972)]. Particular attention is paid to Π electronic states. Perturbative formulas are derived for several coupling cases. The model is checked by means of ab initio calculations at various levels of sophistication. Results of computations of various quantities related to the model are presented for the X 2Πu states of B2H+2 and C2H+2. The reliability of the basis assumptions is demonstrated by comparing the results obtained in the framework of the model considered with those of independent ab initio calculations. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472641
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