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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of sodium-doped polyacetylene (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 634-644 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low-frequency dynamics (〈20 meV) of pure and sodium-doped trans polyacetylene are investigated using a combination of incoherent neutron scattering spectroscopy and molecular dynamics simulations. The simulations are performed using a molecular mechanics potential function and including explicitly the three-dimensional crystal environments of the molecules. Both the experiments and the simulations indicate that doping results in a marked change in the vibrational density of states of the polyene chains in the direction perpendicular to the chain axes, a broad minimum appearing at ∼16 meV. This spectral region is dominated by intramolecular torsional displacements. The results also suggest that the mean-square displacements of the polyacetylene atoms become more isotropic on doping. The contributions of various rigid-body motions to the simulation-derived mean-square displacements and vibrations are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468119
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  • 2
    Electronic Resource
    Electronic Resource
    The polarized density of states of crystalline polyacetylene. Molecular dynamics analysis and comparison with neutron scattering results (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 5586-5596 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The low-frequency (〈20 meV) polarized vibrational density of states in crystalline polyacetylene has recently been derived from inelastic neutron scattering data [J. L. Sauvajol, D. Djurado, A. J. Dianoux, N. Theophilou, and J. E. Fischer, Phys. Rev. B 43, 14 305 (1991)]. The spectral profiles were found to be highly anisotropic and to vary considerably with the chain conformation (cis or trans). Here we investigate the characteristics of the low-frequency vibrations using the molecular dynamics method. Densities of states are calculated from the simulations and directly compared with the data derived from the experiments. The anisotropic and conformation-dependent profiles are mostly well reproduced. The simulation trajectories are further analyzed so as to determine the dynamical contributions to the observed spectra. The lowest-frequency vibrations parallel to the chain axes, at 1.5 meV in the cis system and 4 meV in the trans system, are found to result from whole-molecule rigid-body translations, invariant with chain length. Conversely, the low-frequency intramolecular vibrations are weakly dependent on chain conformation but vary strongly with the chain length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465951
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  • 3
    Electronic Resource
    Electronic Resource
    Raman investigation of rotational and translational excitations in K1−x(NH4)xI mixed crystals (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 4896-4903 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using Raman scattering experiments we have investigated the rotational and translational modes in K1−x(NH4)xI mixed crystals for ammonium concentrations x=0.005, 0.07, 0.16, and x=0.46 and in a fully deuterated isomorph with x(D)=0.42. The A1g+4Eg and T2g Raman responses have been measured at atmospheric pressure in the paraelectric plastic phase (T=295 K) and in the orientational glassy phase (T=7 K). In the low-frequency region ν=5–600 cm−1, seven Raman active components could be identified. These bands are entirely due to the admixture of anisotropic NH+4 to pure KI. Their contributions result either from reorientations of the molecules between equivalent directions and rotational-like excitations around these preferential orientations, or from translational modes of the whole Brillouin zone. In this peculiar case, orientational disorder of the ammonium lifts wave vector conservation of the scattering processes. An interpretation of the different Raman allowed transitions is proposed. The composition and polarization dependences as well as the effect of deuteration for these modes are discussed with respect to earlier reports.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462779
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  • 4
    Electronic Resource
    Electronic Resource
    Structure of 1-fluoroadamantane, C10H15F, in its plastic phase (1982)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 38 (1982), S. 1984-1989 
    Details
    ISSN: 1600-5740
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567740882007729
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  • 5
    Electronic Resource
    Electronic Resource
    A symmetry-adapted-function analysis of plastic crystals. Application to 1-cyanoadamantane at room temperature (1981)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 37 (1981), S. 97-104 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: X-ray diffraction of plastic crystals is investigated by using the decomposition of the orientational average density of the atoms on symmetry-adapted functions. For a cubic lattice, the molecular librational amplitude is related to the order of the cubic harmonics to be used. For a rigid molecule with 3m symmetry in a cubic lattice, the symmetry-adapted functions and the rotator functions are given up to order 12. The plastic phase structure of 1-cyanoadamantane, C11H15N, which is f.c.c., Z = 4 and a = 9.813 (3) Å, has been studied in the Fm3m space group. The orientational average density of the cyano group has a very sharp maximum in the [001] directions not completely describable (Rw = 15.4%) with cubic harmonics of order only up to 12. All the results obtained with this method agree very well with the corresponding ones from the Frenkel model structure of this compound.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S056773948100017X
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  • 6
    Electronic Resource
    Electronic Resource
    Diffraction by finite-size crystalline bundles of single wall nanotubes (1999)
    Springer
    The European physical journal 10 (1999), S. 263-270 
    Details
    ISSN: 1434-6036
    Keywords: PACS. 61.12.Bt Theories of diffraction and scattering - 61.10.Dp Theories of diffraction and scattering - 61.46.+w Clusters, nanoparticles, and nanocrystalline materials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: We calculate the diffraction spectrum of finite-size crystalline bundles of single wall carbon nanotubes (SWNT). The general profile of the spectrum as well as the width and position of the (1 0) diffraction peaks of the 2-D lattice of bundles depend on the tubes symmetry, distribution of tubes diameters and diameter of the bundles. Consequently, any attempt to derive the mean-diameter of the tubes from a diffraction spectrum requires to consider the diameters distribution of the tubes and the size of the bundles. Experimental diffraction profiles of various single wall nanotubes samples are well fitted by the calculated spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100510050854
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  • 7
    Electronic Resource
    Electronic Resource
    Raman study of structural defects in SiO2 aerogels (1995)
    Springer
    Journal of sol gel science and technology 5 (1995), S. 167-172 
    Details
    ISSN: 1573-4846
    Keywords: silica aerogels ; Raman spectroscopy ; structural defects ; 29Si NMR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The structure of the silica aerogels was studied by Raman spectroscopy. The spectra of the solid network resembles that of bulk silica with additional bands related to organic groups and a large amount of OH groups. The typical bands due to ring breathing also called defect bands D 1 and D 2 located at 490 and 610 cm−1 are present. However, the evolution of the D 2 band compared to that of OH band (980 cm−1) seems apparently, in contradiction with the results previously reported in the literature. During heat treatments between 25 and 300°C the D 2 and the OH bands increase simultaneously. Generally, in silica glass the defect band D 2 grows at the expense of the OH groups. This result is explained by the oxidation of the organic compounds which, in this temperature range, leads to the formation of the both species (OH) and those related to siloxane rings. 29Si MAS NMR results are in agreement with the Raman study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00487013
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  • 8
    Electronic Resource
    Electronic Resource
    Localization of the amide group energy in acetanilide: Amide-V vibrations (1995)
    Springer
    Journal of biological physics 21 (1995), S. 25-36 
    Details
    ISSN: 1573-0689
    Keywords: Localized modes ; amide vibrations ; acetanilide ; infrared absorption
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Detailed infrared absorption measurements on acetanilide (ACN) and six specifically deuterated or fluorinated species show at low temperature a very strong anharmonic intensity of the amide-V or N-H out-of-plane bending mode at 500–800 cm−1. The temperature dependence of this band is studied and discussed within the frame of the existing theoretical models proposed for ACN spectra. The features of this anomalous behaviour are consistent with the hypothesis of intrinsic localized modes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00701007
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  • 9
    Electronic Resource
    Electronic Resource
    Temperature dependence of the Raman spectrum of fully deuterated acetanilide (1989)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 20 (1989), S. 517-521 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature dependence of the Raman scattering from a single crystal of acetanilide (ACN-H) and fully deuterated acetanilide (ACN-D) in the low-frequency (phonon) and C=O stretching regions was studied. The observed normal behaviour of the frequency shift of the C=O stretching modes in ACN-D, raises questions concerning several theoretical models previously proposed to explain the peculiar behaviour with temperature of the A1g stretching modes observed in ACN-H. The forms of the low-frequency Raman spectra for ACN-H and ACN-D are very similar, except in the frequency range 70-120 cm-1, where an additional mode (denoted D′) is seen in the Raman spectrum of ACN-D. A strong temperature dependence of the frequency of this band is observed. The origin of this mode is still undecided.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250200807
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  • 10
    Electronic Resource
    Electronic Resource
    Temperature dependence of Raman active modes in triethylenediamine (1982)
    Chichester [u.a.] : Wiley-Blackwell
    Journal of Raman Spectroscopy 13 (1982), S. 270-275 
    Details
    ISSN: 0377-0486
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The temperature dependence of Raman active modes in monocrystalline Triethylenediamine has been studied by Raman spectroscopy. The linewidths and frequencies of these modes have been measured in the temperature range 110-330 K (that is the low temperature phase for which T 〈 Tc = 351 K). A strong broadening is observed at higher temperatures in this range for the A2 and E1g librons. This can be related to the activation of disorder in the low temperature phase.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jrs.1250130312
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