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  • 1
    Electronic Resource
    Electronic Resource
    Acetaldehyde: Harmonic Frequencies, Force Field, and Infrared Intensities (1995)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 99 (1995), S. 13850-13864 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100038a016
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  • 2
    Electronic Resource
    Electronic Resource
    Flexing analysis of ethane internal rotation energetics (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 4268-4275 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A flexing analysis of the ethane barrier energy in terms of structural (ΔEstruct), steric exchange (ΔEsteric), and hyperconjugative charge-transfer (ΔEdeloc) energy contributions has been carried out using natural bond orbitals. No evidence is found for the view that the ethane staggered equilibrium geometry or the C–C bond expansion that accompanies rotation results from steric exchange repulsion interactions. The analysis shows that ΔEstruct and ΔEdeloc have very different stereoelectronic dependencies, but that the ΔEsteric and ΔEdeloc dependencies are antagonistic. All of their contributions are strongly affected by the C–C bond expansion, with the result that the barrier mechanism cannot be understood without taking into account their different relaxation dependencies. Neglect of C–C expansion leaves the charge-transfer interactions paramount by subduing the steric and structural contributions. These interactions are found to be an important determinant for the expansion. The strong expansion dependence found for ΔEstruct is largely controlled by weakening of the C–C bond, and to a lesser extent by concomitant strengthening of the C–H bonds. Most of this dependence can be mimicked by C–C expansion in the absence of methyl torsion indicating that C–C bond weakening does not arise from the symmetry change accompanying ethane torsion. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478310
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  • 3
    Electronic Resource
    Electronic Resource
    Flexing analysis of steric exchange repulsion accompanying ethane internal rotation (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 72-78 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Relaxation calculations using natural bond orbitals are carried out for the Puali exchange steric repulsion changes associated with ethane internal rotation using sufficiently extended Dunning correlation-consistent and Gaussian orbitals, so that interpretations are not basis set dependent. These calculations show that the total exchange repulsion is strongly dependent on the C–C bond lengthening that accompanies rotation. The effect of this relaxation is that the total exchange repulsion favors the eclipsed conformer by ∼6 kcal/mol, far greater than previous estimates obtained without skeletal relaxation. The source of the skeletal flexing dependence stems from the strong dependence of the orthogonalization-induced-energy-shift of the σCH NBO and carbon core orbitals on RC–C. Strong basis set dependence is found for the pairwise repulsions. Extended basis set calculations attribute an antibarrier energy change to anti/syn repulsions and a barrier-forming one to gauche repulsions. These senses are opposite to the barrier-forming anti/syn CH pairwise interactions found in previous ethane steric considerations. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476541
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  • 4
    Electronic Resource
    Electronic Resource
    Acetone n-radical cation internal rotation spectrum: The torsional potential surface (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 2762-2768 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The one color REMPI and two color ZEKE-PFI spectra of acetone-d3 have been recorded. The 3px Rydberg state of acetone-d3 lies at 59 362.3 cm−1 and both of the torsional modes are visible in this spectrum. The antigearing Rydberg (a2) mode, v12*, has a frequency of 62.5 cm−1, while the previously unobserved gearing (b1) mode, v17*, is found at 119.1 cm−1. An ionization potential of 78 299.6 cm−1 for acetone-d3 has been measured. In acetone-d3 n-radical cation ground state, the fundamentals of both of the torsional modes have been observed, v12+ at 51.0 cm−1 and v17+ at 110.4 cm−1, while the first overtone of v12+ has been measured at 122.4 cm−1. Deuterium shifts show that v12+ behaves like a local C3v rotor, but that v17+ is canonical. Combining this data with that for acetone-d0 and aacetone-d6 has allowed us to fit the observed frequencies to a torsional potential energy surface based on an ab initio C2v cation ground state geometry. This potential energy surface allows for prediction of the v17 vibration in acetone-d0 and acetone-d6. The barrier to synchronous rotation is higher in the cation ground state than in the neutral ground state, but significantly lower than in the 3s Rydberg state. The 3px Rydberg and cation ground state potential energy surfaces are found to be very similar to each other, strongly supporting the contention that the 3px Rydberg state has C2v geometry and is a good model for the ion core. The altered 3s Rydberg state potential surface suggests this state has significant valence character. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480850
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  • 5
    Electronic Resource
    Electronic Resource
    Sign of V6 term in internal rotation potential of acetaldehyde. Theory and experiment in harmony (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1274-1277 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The V6 term, regulating the shape of the internal rotation potential for a single rotor, has been predicted by ab initio theory for acetaldehyde. The internal rotation potential constants were computed by single point fourth order Møller–Plesset (MP4) 6-311G(3df,2p) level theory for three models differing in molecular flexing motions using MP2 optimized molecular geometries. The negative sign of V6, established by microwave and infrared experiments, is predicted only by the fully relaxed model which includes out-of-plane wagging of the aldehyde hydrogen. This requires strong coupling of methyl torsional motion to the hydrogen wag. The predicted magnitude of V6 differs by only 4 cm−1 from the experimentally established value.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466656
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  • 6
    Electronic Resource
    Electronic Resource
    Two-photon spectra of aromatic molecules (1984)
    s.l. : American Chemical Society
    Accounts of chemical research 17 (1984), S. 250-257 
    Details
    ISSN: 1520-4898
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ar00103a005
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  • 7
    Electronic Resource
    Electronic Resource
    The a2g mode in ground state benzene (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1479-1487 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Harmonic ground state frequencies for the a2g mode, ν3, in C6H6, C6D6, and 13C6H6 have been determined by application of the Teller–Redlich product rule to b2u mode frequencies obtained from two-photon fluorescence excitation experiments for the D6h symmetry molecules and a′2 frequencies from 1,3,5-C6H3D3 determined at rotational contour resolution. The a2g harmonic frequency values are 1366.6 cm−1 for C6H6, 1063.0 cm−1 for C6D6, and 1355.4 cm−1 for 13C6H6. The anharmonic correction to ν3 in C6H6, estimated from the difference in product rule and infrared frequencies is −17 cm−1. The b2u mode frequencies, ν14 and ν15, respectively, have also been significantly modified from those obtained from lower resolution spectra to 1309.4 and 1149.7 cm−1 in C6H6, 1286.3 and 827.9 cm−1 (harmonic value) in C6D6, and 1269.8 and 1138.1 cm−1 in 13C6H6. The anharmonic correction for ν15 in C6D6 is estimated as −4 cm−1. The B2u←A1g electronic origin of 13C6H6, has been determined for the first time as 38 105.5±0.3 cm−1. The B2u←A1g electronic origin of 1,3,5-C6H3D3 has been redetermined to be 38 187.5±0.3 cm−1, 3.5 cm−1 higher than previously reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453257
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  • 8
    Electronic Resource
    Electronic Resource
    Erratum: Complete harmonic force field for benzene ground state in-plane vibrations [J. Chem. Phys. 83, 6047 (1985)] (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2346-2347 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451864
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  • 9
    Electronic Resource
    Electronic Resource
    Acetone n-radical cation conformational preference and torsional barrier (2002)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 116 (2002), S. 7049-7056 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The ab initio architecture and torsional barrier for acetone n-radical cation are obtained. The 923 cm−1 MP4/6-311+G(3df,2p) barrier is calculated to be 30% higher than for neutral acetone. This increase is largely attributed to correlation effects and less importantly to increased hyperconjugative stabilization of the equilibrium cation conformer. Ionization is predicted to cause opening of the central CCC angle by 7° and cause the methyl groups to lose the C3v symmetry that they possess in neutral acetone. The torsional coordinate for the infrared active b1 (gearing) rotation is predicted to not lie purely on the torsional potential surface, but to be contaminated by puckering of the CCCO skeleton in both the neutral and cation species, thereby making the b1 infrared torsional frequencies only partially suitable for sampling the torsional potential surface. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1463438
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  • 10
    Electronic Resource
    Electronic Resource
    The benzene ground state potential surface. I. Fundamental frequencies for the planar vibrations (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 84 (1986), S. 6642-6656 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The accuracy of vapor phase vibrational data has been improved for all 12 deuterium-labeled benzenes and for 13C12C5H6 and 13C6H6. Many vapor phase fundamental frequencies are observed for the first time. Precise isotopic frequency/splitting patterns for ν1, ν18, and ν19 have been obtained. Isotope induced harmonic mode mixing matrices are given for all 14 labeled benzenes and used to provide detailed description of the fundamental bands observed in the spectra. These descriptions provide numerous reassignments for the fundamental bands, particularily in low symmetry deuterium benzenes. The matrices show that some skeletal modes, such as ν1, gain CH stretching character as a result of deuterium labeling, providing a rationalization for the increased anharmonicity observed in recent jet experiments for C6D6. In addition, a reassessment of Fermi resonance gives 3072.3 cm−1 for the unperturbed frequency (correction +24 cm−1) for the e1u mode ν20 in C6H6 refining the CH local mode anharmonic constant, 2xii, to 117.5 cm−1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.450717
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