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  • 11
    Electronic Resource
    Electronic Resource
    Silaketene: A product of the reaction between silylene and carbon monoxide? (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1031-1035 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Molecular structures and vibrational frequencies for silaketene, H2SiCO, are predicted using ab initio techniques. A weakly bound nonplanar structure is found to be the equilibrium geometry, whereas the ketene-like planar structure is the transition state for inversion between the two equivalent nonplanar conformations. The barrier to inversion about the silicon atom is 18 kcal/mol. The ab initio heat of reaction of SiH2 and CO to form H2SiCO is 16 kcal/mol. The results are discussed in light of recent matrix isolation experiments attempting to make and detect dimethylsilaketene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456155
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  • 12
    Electronic Resource
    Electronic Resource
    Structure and energetics of the lowest 1A1 and 1B1 states of dichlorocarbene (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 2063-2067 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A recent (1989) partial structural analysis of spectroscopic measurements by Choe, Tanner, and Harmony led to the conclusion that the first excited electronic state (1B1 state) of CCl2 has a longer bond distance than does the 1A1 ground state. This is consistent with typical Franck–Condon pictures of diatomic potential curves and with experimental results for the analogous CF2 system. However, the earlier (1985) theoretical study of Nguyen, Kerins, Hegarty, and Fitzpatrick came to the qualitatively opposite conclusion, predicting the 1B1 bond distance to be shorter by 0.044 A(ring), which agrees with the 1989 analysis of rotationally resolved spectra by Clouthier and Karolczak. In this research high level ab initio quantum mechanical methods are used to clarify this question. The most reliable values predicted here for the CCl2 bond distances are r0=1.713 A(ring) (1A1) and r0=1.657 A(ring) (1B1). Large basis sets and high levels of electron correlation are required for excellent agreement with experiment in both structures and energies. The differences between CF2 and CCl2 in the behavior of the C–X bond length upon excitation is discussed. It is also argued that most closed shell carbenes are not two configuration problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459928
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  • 13
    Electronic Resource
    Electronic Resource
    Classical and nonclassical forms of the vinyl cation: A coupled cluster study (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 3653-3658 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The energy difference between the classical and nonclassical forms of the vinyl cation is studied using the single and double excitation configuration interaction (CISD) and coupled cluster methods (CCSD and CCSDT-1). The basis sets employed range from double ζ to those including f functions on carbon and d functions on hydrogen. It is shown that the theoretical energy differences are very sensitive to the inclusion of higher-order polarization functions and the inclusion of triple excitations in the correlated wave functions. The results are compared with other theoretical studies in the literature and with the very recent experimental work of Crofton, Jagod, Rehfuss, and Oka. The most reliable single theoretical treatment involves the CCSDT-1 method with basis set C(10s5p2d1f/4s3p2d1f), H(5s2p/3s2p), and predicts 3.3 kcal/mol for the classical/nonclassical energy difference. Basis set extension is expected to increase this separation to about 4.0 kcal/mol, still less than the experimental value, 〉6 kcal/mol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457821
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  • 14
    Electronic Resource
    Electronic Resource
    Infrared absorption of cis- and trans-alkali-metal peroxynitrites (MOONO, M=Li, Na, and K) in solid argon (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 4026-4034 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potassium nitrate (KNO3) isolated in solid argon at 13 K was irradiated with emission from an ArF excimer laser at 193 nm. Recombination of the photofragments led to formation of both cis- and trans-potassium peroxynitrites (KOONO). The cyclic conformer, cis-KOONO, absorbs at 1444.5, 952.3, 831.6, and 749.1 cm−1, whereas trans-KOONO absorbs at 1528.4, 987.4, and 602.2 cm−1. The assignments are based on observed 18O- and 15N-isotopic shifts and comparison with similar compounds, cis–cis and trans–perp HOONO. Ab initio calculations using density functional theory at a Becke3LYP level predicted similar line positions and isotopic shifts for both conformers. Photoconversion among these three isomers was achieved at various wavelengths and periods of irradiation; cis-KOONO was photolyzed readily at 308 nm, whereas trans-KOONO increased slightly in intensity initially and was eventually transformed to KNO3 on prolonged irradiation. Similar results were obtained for LiNO3 and NaNO3; cis-LiOONO and cis-NaOONO absorb at (1423.4, 1422.0), 966.2, 874.2, 792.3 cm−1 and (1437.4, 1434.6), 961.4, 840.7, (770.9, 768.7) cm−1, respectively, whereas trans-LiOONO and trans-NaOONO absorb at (1581.6, 1580.4), (998.3, 995.6), 600.4 cm−1 and (1549.3, 1540.6), (996.3, 994.1), (609.4, 607.4) cm−1, respectively; the numbers in parentheses are due to line splitting. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469588
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  • 15
    Electronic Resource
    Electronic Resource
    Vinylidene radical cation: a sizable barrier to unimolecular rearrangement to the acetylene radical cation (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 7560-7562 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100359a010
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  • 16
    Electronic Resource
    Electronic Resource
    Oxywater (water oxide): new evidence for the existence of a structural isomer of hydrogen peroxide (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 9250-9254 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100202a034
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  • 17
    Electronic Resource
    Electronic Resource
    Ab initio force constants and the reassignment of the vibrational spectra of all-trans- and all-cis-1,3,5,7-octatetraene (1989)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 93 (1989), S. 2341-2347 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100343a029
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  • 18
    Electronic Resource
    Electronic Resource
    Methylphosphinidene (CH3P) and its rearrangement to phosphaethylene (CH2PH): toward the observation of ground-state triplet CH3P (1993)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 97 (1993), S. 1872-1877 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100111a026
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  • 19
    Electronic Resource
    Electronic Resource
    Ammonia alane (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5310-5317 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio studies employing basis sets approaching triple-ζ plus double-polarization plus f function quality are reported for AlH3NH3, AlH3, and NH3. The self-consistent-field method was employed for all basis sets; the single and double excitation configuration interaction and the comparable coupled-cluster methods were utilized with a double-ζ plus polarization functions basis set. The dissociation energy of AlH3NH3 is predicted to be 26 kcal/mol after correcting for zero-point vibrational energy, in qualitative agreement with the rough estimate of 30 kcal/mol by Haaland for Al–N bond strengths. In keeping with the dative nature of the Al–N bond, the AlH3 and NH3 moieties do not undergo large changes upon the formation of AlH3NH3. The resemblance of AlH3NH3 to the related compound BH3NH3 is quite strong. The equilibrium geometry, harmonic vibrational frequencies, infrared intensities, atomic charges, and dipole moment of ammonia alane are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462716
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  • 20
    Electronic Resource
    Electronic Resource
    Direct inversion in the iterative subspace (DIIS) optimization of open-shell, excited-state, and small multiconfiguration SCF wave functions (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 5728-5734 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The direct inversion in the iterative subspace (DIIS) method is applied to several simple SCF wave functions in an effective Fock matrix formulation. The following cases are treated: high-spin-restricted open shell, open-shell singlet, and two-configuration wave functions. Open-shell singlet states are described by a three-determinant 2×2 CAS expansion which is equivalent to Davidson's nonorthogonal SCF method in the case of the first open-shell singlet. Very sharp convergence is usually obtained in less than 20 cycles. The method is applicable to slowly convergent or even inherently divergent cases, and able to enforce convergence to excited states not the lowest of their symmetry. For these simple wave functions, the present first order method is asymptotically more efficient than second-order methods. Examples are presented for H2O, H2O2, C2H4, F2, several states of NO2, C2H5, formaldehyde, and ketene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449880
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