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  • American Institute of Physics (AIP)  (4)
  • 1
    Electronic Resource
    Electronic Resource
    The vibration and orientation bands of the NH+4 ion in ammonium tetraphenylborate. IV. Raman studies (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7632-7638 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The N–H stretching and low frequency regions of the Raman spectrum of the title compound [ammonium tetraphenylborate (ATPB) and ATPB-d20 ] are examined at low temperatures. In the low frequency Raman region, we observe the predicted orientational transitions directly. The Raman N–H spectrum shows features similar to those in the infrared spectrum of this region, interpreted as showing nearly free rotation of the NH+4 ions. Many of the features of both the low frequency and N–H stretching regions arise from the effect of D2d site symmetry on the otherwise tetrahedral NH+4 ion. The picture of some of the NH+4 ions in this crystal as perturbed, but very nearly free to rotate is confirmed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459394
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  • 2
    Electronic Resource
    Electronic Resource
    Quantum rotations of the ammonium ions in ammonium tetraphenyl–borate. III. Inelastic neutron scattering results (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8963-8967 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Incoherent inelastic neutron scattering experiments have been performed on polycrystalline samples of NH4B(C6H5)4 and NH4B(C6D5)4 in the 1.5–120 K temperature range. A high-resolution inelastic neutron scattering spectrum at the lowest temperatures reveals a rotational tunneling spectrum containing two peaks at 26.5 and 53.0 μeV and is characteristic of ammonium ions in a cubic environment. From the intensities of these peaks it seems that about half of the ammonium ions are involved in this tunneling. Two further peaks are found at higher energy, 4.3 and 8.2 meV, either of which may be correlated as the libration associated with the observed tunnel splitting depending on the form of the potential. An alternative assignment of the peaks at 4.3 and 8.2 meV as transitions of a free rotor from the ground state to the J=2 and J=3 levels is also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459235
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  • 3
    Electronic Resource
    Electronic Resource
    The crystalline site symmetry and its effect on the vibrational spectra of a weakly hindered molecule. V. Crystallization effects in NH4B(C6H5)4 (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 8524-8534 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Changes in the vibrational spectra for molecules that nearly freely rotate or perform rotational tunneling at low temperatures are explained through the systematic study of the combined symmetry of the molecule, the site, and the molecule's nuclear spins. The changes observed for different crystallizations in the low temperature vibrational spectra of the NH+4 ion dilute in KTPB and in NH4B(C6D5)4, the NH3D+ ion in ATPB and NH4ClO4, and of solid CH4 II are examined and explained as arising from slight perturbations of the crystalline site symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459290
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  • 4
    Electronic Resource
    Electronic Resource
    The libration–vibration bands of the ammonium ion in ammonium tetraphenylborate: Evidence for nearly free rotation (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 6393-6405 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The N–H stretching and H–N–H bending regions of the infrared spectrum of the title compound (ATPB) have been examined with care. The stretching bands show rotation-like structure that we attribute to rotational motion of NH+4 in a very low barrier. The barrier has the symmetry of a tetrahedral molecule in a tetrahedral site and is characterized by the dimensionless parameter β=1. The J=0 and J=1 levels are below the barrier and the J=2 levels are above it. Slow interconversion of nuclear spin species is seen in keeping with the low barrier model. The spectra of the ATPB with some NH3D+, with a high concentration of K+ and with deuterated phenyl groups have been examined, and show spectra in keeping with the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453470
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