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  • 1
    Electronic Resource
    Electronic Resource
    Refined thermochemistry for the methanol radical cation (CH3OH.cntdot.+) and its distonic isomer (CH2OH2.cntdot.+) (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 5804-5807 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100193a029
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  • 2
    Electronic Resource
    Electronic Resource
    New Theoretical and Experimental Proton Affinities for Methyl Halides and Diazomethane: A Revision of the Methyl Cation Affinity Scale (1994)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 98 (1994), S. 13099-13101 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100101a001
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  • 3
    Electronic Resource
    Electronic Resource
    Gaussian-2 (G2) theory: Reduced basis set requirements (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 5148-5152 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Two variations of G2(MP2) theory which employ smaller basis sets in evaluating the quadratic configuration interaction [QCISD(T)] component of the energy are presented. The first, G2(MP2,SVP), uses the split-valence plus polarization (SVP) 6-31G(d) basis, while the second, G2(MP2,SV), uses the split-valence (SV) 6-31G basis. The methods are evaluated on the basis of results for the set of 125 systems used for testing G2 theory. The mean absolute deviation of G2(MP2,SVP) results from experimental values is 1.63 kcal mol−1 compared with 1.58 and 1.21 kcal mol−1 for G2(MP2) and G2, respectively. The G2(MP2,SVP) method thus provides results which are generally very similar in quality to those obtained from G2(MP2) but at considerably reduced computational expense. On the other hand, the mean absolute deviation of G2(MP2,SV) results from experiment is substantially larger (2.13 kcal mol−1). The G2(MP2,SV) method exceeds the 2 kcal mol−1 target accuracy of G2 theory for an unacceptably large number of comparisons. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471141
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  • 4
    Electronic Resource
    Electronic Resource
    Theoretical and experimental structures of vinyl chloride and vinyl bromide (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 3952-3959 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structures of vinyl chloride and vinyl bromide have been determined by ab initio molecular orbital calculations, and corrections applied to obtain theoretical r0 values. The theoretical r0 structures agree very well with experimental r0 structures derived from recent microwave spectral data. This contrasts with the situation for vinyl alcohol and vinyl fluoride for which significant discrepancies have been found between theoretical and experimental estimates of the CCHu angles involving the hydrogen atom geminal to the substituted center. The present results reinforce our earlier conclusion that the theoretical values for this parameter for vinyl alcohol and vinyl fluoride are more reliable than the experimental values. Difficulties in the experimental structural determinations for vinyl fluoride and vinyl alcohol are attributed to the unusual insensitivity of the experimental moments of inertia to the values of the CCHu angles, resulting in turn from the close proximity to a principal inertial axis of two of the atoms that define the CCHu angles in these molecules. In contrast, all three atoms defining the CCHu angles in vinyl chloride and vinyl bromide are far removed from the inertial axes. As a consequence, the experimental moments of inertia are sensitively dependent on the value of the CCHu angle, and theoretical and experimental structures agree well. We conclude that suggestions that substituted ethenes present unusual difficulties for ab initio structural determinations are unfounded. Sensitivity curves are suggested as valuable indicators of potential problems in experimental structural determinations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.464022
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  • 5
    Electronic Resource
    Electronic Resource
    Transition structures for the interchange of hydrogen atoms within the water dimer (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 1240-1247 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High levels of ab initio molecular orbital theory were used to examine rearrangement processes in the water dimer corresponding to the interchange of various hydrogen atoms. Our most reliable calculations involve MP4/6-311+G(2df,2p) energy evaluations at MP2/6-311+G(d,p) optimized structures. The lowest energy rearrangement pathway corresponds to the interchange of hydrogen atoms of the acceptor molecule within the Cs water dimer structure (1). This proceeds via a transition structure of C1 symmetry (2) and requires an energy of 0.59 kcal mol−1. The interchange of donor and acceptor molecules can be achieved via a transition structure with Ci symmetry (4) and requires an energy of 0.87 kcal mol−1. Finally, the interchange of hydrogen atoms of the donor molecule, via a C2v transition structure (9), requires 1.88 kcal mol−1. The rearrangements via 2 and 4 lead to complete scrambling of hydrogen atoms within the individual H2O moieties at a cost of 0.87 kcal mol−1; the transition structure 9 is not necessary for this process. The implications of these results with regard to the interpretation of spectroscopic data on the water dimer will be of interest.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.458133
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  • 6
    Electronic Resource
    Electronic Resource
    Potential energy surfaces describing ion complexes containing molecular hydrogen (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 1191-1210 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High-level ab initio molecular orbital calculations have been carried out to describe the potential energy surfaces for a series of systems corresponding formally to dimer ions of molecular hydrogen with an inert-gas atom or a first- or second-row hydride [X⋅⋅⋅H2](overdot) +, where X=He, Ne, Ar, Kr, HF, HCl, H2O, H2S, NH3, and PH3. Of the [XH2](overdot) + ion complexes, [Ne⋅⋅⋅H2](overdot) +, [Ar⋅⋅⋅H2](overdot) +, [Kr⋅⋅⋅H2](overdot) +, and [HFH⋅⋅⋅H](overdot) + lie in wells of significant depth and should be experimentally observable. The energetics of ion–molecule reactions associated with the [XH2](overdot) + systems have been examined in detail. The reactions include proton- and hydrogen-transfer reactions and hydrogen-exchange reactions. Pathways and transition structures for scrambling of hydrogen atoms within the [XH2](overdot) + complexes, some of which are relevant to the exchange reactions, have also been determined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463246
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  • 7
    Electronic Resource
    Electronic Resource
    Characterization of the bifurcated structure of the water dimer (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 95 (1991), S. 1825-1828 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The bifurcated structure of the water dimer has been the subject of considerable uncertainty with respect to its vibrational characterization. We have considered this question at the self-consistent-field (SCF) level of theory using finite basis sets that allow a close approach to the Hartree–Fock limit. As one approaches the Hartree–Fock limit, the bifurcated structure is predicted to be a true transition state, with one imaginary vibrational frequency, ω12(B2)∼200i cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.461030
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical and experimental structures of vinyl fluoride and vinyl alcohol (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 97 (1992), S. 6113-6120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new theoretical r0 structure for vinyl fluoride has been derived using ab initio molecular orbital procedures. In addition, new experimental r0 and rs structures have been obtained through a reanalysis of existing experimental microwave data. Significant discrepancies are found between the new theoretical (125.4°) and experimental (127.6°) r0 estimates of the CCHu angle involving the hydrogen atom geminal to the substituted center. This is attributed to the relative insensitivity of the experimental structural fits to the precise value of this bond angle, an insensitivity that is associated with the proximity of the relevant atoms to inertial axes. Because of these difficulties, the best estimate of the experimental r0 structure for vinyl fluoride is obtained by taking the theoretical r0 value for the CCHu angle and determining the remaining parameters by a weighted-least-squares fit to the experimental data. Weighted-least-squares fits are found generally to provide more consistency in the derived structural parameters than unweighted procedures. It is found that fitting of isotopic differences in rotational constants (as opposed to the conventional fitting of rotational constants themselves) provides the structure for vinyl fluoride most similar to the theoretical r0 structure. Similar observations are found to hold for vinyl alcohol, for which new theoretical and experimental results are presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.463721
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  • 9
    Electronic Resource
    Electronic Resource
    Unimolecular rearrangements connecting hydroxyethylidene (CH3-C-OH), acetaldehyde (CH3-CH:O), and vinyl alcohol (CH2:CH-OH) (1991)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 113 (1991), S. 6452-6458 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00017a015
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  • 10
    Electronic Resource
    Electronic Resource
    Rearrangement and dissociative reactions of the methanol radical cation (CH3OH.bul.+): a comparison of theory and experiment (1991)
    s.l. : American Chemical Society
    Journal of the American Chemical Society 113 (1991), S. 7903-7912 
    Details
    ISSN: 1520-5126
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ja00021a013
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