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  • AIP Publishing  (30)
  • Allen, Leland C.  (30)
  • 1
    Online Resource
    Online Resource
    Internal Rotation Barriers for Hydrazine and Hydroxylamine from Ab Initio LCAO—MO—SCF Wavefunctions
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 47, No. 3 ( 1967-08-01), p. 895-905
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 47, No. 3 ( 1967-08-01), p. 895-905
    Abstract: LCAO—MO—SCF ab initio wavefunctions with atomic basis orbitals of double-zeta accuracy have been constructed for N2H4 and NH2OH and the potential-energy curves versus internal-rotation angle have been determined. Similar wavefunctions for CH3CH3, CH3OH, CH3NH2, and H2O2, reported previously, showed a quantitatively useful correlation with experimental barrier heights and shapes. Since experimental information on the N2H4 and NH2OH barriers is incomplete or unknown, the theoretical results presented here may help guide experimental work. Decomposition of the total energy into one- and two-electron components has been found previously to help elucidate the physical origin of the rotational barrier, and results for the species studied here are given. The wavefunctions presented here (and those reported previously for the species noted above) are the most accurate available for molecules possessing a rotational barrier about a single bond, and comparison is made with the results of the other existing ab initio wavefunctions.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1712054
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 2
    Online Resource
    Online Resource
    Electronic Structure and Geometry of Hydrogen Cyanide
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 5 ( 1967-03-01), p. 1797-1803
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 5 ( 1967-03-01), p. 1797-1803
    Abstract: The geometry and charge distribution of HCN in its ground state has been determined by means of many-electron, self-consistent-field molecular-orbital wavefunctions. LCAO MO SCF calculations and ones which split the AO's with linear variation coefficients yield properties and total energies reasonably close to the molecular Hartree—Fock limit. A linear molecule with bond distances correct to 1% of the microwave spectroscopy values is obtained. Walsh's orbital-energy diagrams are found to be almost independent of angle but with nearly compensating variations and for this molecule Walsh's orbital-energy summation criterion leads to a bent ground state. This result, however, is easily understood in terms of the relatively high ionic character of the H–CN bond. An empirical molecular bind energy correlation scheme based on diatomic molecular Hartree—Fock solutions is employed to analyze the difference between the computed (7.10 eV) and the experimental (13.53 eV) binding energy values.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1840937
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
    Online Resource
    Online Resource
    Resolution Enhancement for Spectra of Chemical and Physical Interest
    AIP Publishing ; 1964
    In:  The Journal of Chemical Physics Vol. 40, No. 11 ( 1964-06-01), p. 3135-3141
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 40, No. 11 ( 1964-06-01), p. 3135-3141
    Abstract: When a spectrum is composed of a superposition of lines with known shape and uniform width, the signal output of a spectrometer may be transformed into a spectrum whose effective resolution is significantly improved. If the line shapes are not precisely known or the linewidths not exactly uniform, it is still possible to achieve a worthwhile resolution enhancement. Decomposition and analysis of complex spectra is often aided by this transformation. The theory of filters which produce the desired transformation is developed. Digital and analog implementation for these filters is given as well as several examples.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1724976
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1964
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
    Online Resource
    Online Resource
    Rotational Barriers in Hydrogen Peroxide
    AIP Publishing ; 1971
    In:  The Journal of Chemical Physics Vol. 55, No. 2 ( 1971-07-15), p. 519-527
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 55, No. 2 ( 1971-07-15), p. 519-527
    Abstract: The rotational barriers in hydrogen peroxide are investigated using LC(Hartree–Fock) AO MO SCF calculations. Systematic improvement of the basis set produces a definite trans barrier, demonstrating that this barrier, like all those previously studied, is calculable within the Hartree–Fock approximation. Allowance for geometry adjustment, particularly OOH angle variation, leads to a cis barrier much closer to agreement with experiment than that obtained assuming rigid rotation. The theoretical and experimental inplications of these findings are discussed.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1675782
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1971
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 5
    Online Resource
    Online Resource
    Proton chemical shift tensors in hydrogen-bonded dimers of RCOOH and ROH
    AIP Publishing ; 1983
    In:  The Journal of Chemical Physics Vol. 79, No. 10 ( 1983-11-15), p. 4958-4966
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 79, No. 10 ( 1983-11-15), p. 4958-4966
    Abstract: In an effort to explain empirically observed correlations between certain structural features of hydrogen bonds and corresponding proton chemical shift parameters determined by single crystal multiple pulse NMR, a theoretical investigation is made of 14 O–H⋅⋅⋅O dimers involving substituted carboxylic acids and alcohols. Nuclear magnetic shielding tensors are calculated for the protons in each hydrogen bond system. Certain linear dependences are observed, in agreement with experimental data, that indicate that the chemical shift tensor is a sensitive measure of hydrogen bonding that can yield more information than the isotropic shift alone. The apparent correlation between the O⋅⋅⋅O separation and isotropic chemical shift is seen to result from the strong dependence of the perpendicular shielding component on the former quantity. The lack of a similar correlation for the chemical shift anisotropy is explained in terms of the parallel component of the shielding tensor. An interpretation of such trends in these proton chemical shift tensors is proposed in terms of existing models of hydrogen bonds.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.445589
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1983
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 6
    Online Resource
    Online Resource
    Numerical Test of the Integral Hellmann—Feynman Theorem
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 8 ( 1967-04-15), p. 3270-3271
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 8 ( 1967-04-15), p. 3270-3271
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1841204
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 7
    Online Resource
    Online Resource
    Gaussian Orbitals for Many-Electron Molecular Wave Functions
    AIP Publishing ; 1962
    In:  The Journal of Chemical Physics Vol. 37, No. 1 ( 1962-07-01), p. 200-201
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 37, No. 1 ( 1962-07-01), p. 200-201
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1732962
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1962
    detail.hit.zdb_id: 3113-6
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  • 8
    Online Resource
    Online Resource
    Erratum: Wavefunctions and Correlation Energies for F, F—, and Ne
    AIP Publishing ; 1963
    In:  The Journal of Chemical Physics Vol. 39, No. 8 ( 1963-10-15), p. 2106-2107
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 39, No. 8 ( 1963-10-15), p. 2106-2107
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1734589
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1963
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 9
    Online Resource
    Online Resource
    Origin of Rotational Barriers. II. Methylamine and Improved Wavefunctions for Hydrogen Peroxide
    AIP Publishing ; 1967
    In:  The Journal of Chemical Physics Vol. 46, No. 6 ( 1967-03-15), p. 2276-2284
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 46, No. 6 ( 1967-03-15), p. 2276-2284
    Abstract: LC(Hartree—Fock) AO MO SCF wavefunctions have been constructed for CH3NH2 and MO SCF wavefunctions beyond this level of approximation for H2O2. Analysis of these solutions along with wavefunctions determined previously for CH3CH3 and CH3OH makes possible several conclusions concerning the origin of rotational barriers: (1) Study of a sequence of molecules, including particularly those of low symmetry, is required for detailed understanding. (2) The origin may be found within the framework of the Hartree—Fock approximation. (3) Decomposition of the total energy into one- and two-electron components elucidates the barrier origin and provides a physical picture of the barrier mechanism as a delicate balance between the interactions of lone pairs, bonds, and protons.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1841032
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1967
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 10
    Online Resource
    Online Resource
    Electronic Wave Functions for Polyatomic Molecules
    AIP Publishing ; 1959
    In:  The Journal of Chemical Physics Vol. 31, No. 3 ( 1959-09-01), p. 736-737
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 31, No. 3 ( 1959-09-01), p. 736-737
    Abstract: A one-electron basis set made from functions with exponential and Gaussian radial dependence is proposed for constructing many-electron, many-center, electronic wave functions. Appropriate mixtures of these two types may greatly simplify the evaluation of many-center, two electron integrals and in addition make possible an improved description of the molecular bond. Plane waves may also be added to the basis set thus making an application to solids appear feasible.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.1730454
    Language: English
    Publisher: AIP Publishing
    Publication Date: 1959
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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