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  • 1
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    Undoped and doped poly(tetraphenylbenzidine) as sensitive material for an impedimetric nitrogen dioxide gas dosimeter (2014)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2014-09-30
    Description: This article presents a nitrogen dioxide (NO 2 ) detecting gas dosimeter based on poly(tetraphenylbenzidine) poly(TPD) as nitrogen oxide (NO x ) sensitive layer. Gas dosimeters are suitable devices to determine reliably low levels of analytes over a long period of time. During NO x exposure, the analyte molecules are accumulated irreversibly in the sensing layer of the dosimeter enhancing the conductivity of the hole conducting poly(TPD), which can be measured by impedance spectroscopy. Due to their possibility for low cost production by simple printing techniques and very good physical, photochemical, and electrochemical properties, poly(TPD)s are suitable for application in gas dosimeters operated at room temperature. We studied the effect of doping with a Co(III)-complex in combination with a conducting salt on the dosimeter behavior. Compared to the undoped material, a strong influence of the doping can be observed: the conductivity of the sensing material increases significantly, the noise of the signal decreases and an unwanted recovery of the sensor signal can be prevented, leading to a NO x detection limit
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics (AIP)
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  • 2
    Electronic Resource
    Electronic Resource
    Proton tunneling in benzoic acid crystals at intermediate temperatures: Nuclear magnetic resonance and neutron scattering studies (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 7300-7311 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dynamics of proton transfer along the hydrogen bonds of dimers of benzoic acid has been characterized in single crystals and powders at temperatures between 10 K and 110 K by quasi-elastic neutron scattering (QENS) and by proton spin-lattice relaxation using field-cycling NMR spectroscopy. These measurements define the geometry of the proton transfer, the energy difference between the two tautomers of benzoic acid corresponding to the two proton positions, as well as the proton correlation time. The proton jump vector agrees well with expectations from recent crystallographic data. The energy difference between tautomers of A/kB=86.5±1.5 K is in contradiction with the lower value of A/kB=50 K derived from older 13C NMR and infrared absorption measurements. NMR and QENS measurements provide mutually consistent values of the proton correlation time, τc, and an accurate characterization of the dynamics at temperatures where the onset of thermally activated processes is observed. Tunneling in an excited vibrational level, as well as multiphonon transitions between the lowest tunneling levels, are expected to contribute to these dynamics and are discussed. The inverse correlation time for the proton dynamics over the entire temperature range between 0 K and ambient temperature is well represented by the expression: 1/τc={1.72×108 coth(43/T)+1010 exp(−180/T)+6.3×1011 exp(−600/T)} s−1. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477407
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  • 3
    Electronic Resource
    Electronic Resource
    Methyl group tunneling—A quantitative probe of atom–atom potentials (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 1725-1731 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A molecular mechanics calculation of the rotational potential experienced by methyl groups in molecular crystals is presented. Good agreement for seven out of the eight cases considered is obtained and the methyl group becomes a quantitative probe of its molecular environment. The calculation is used to gain insight into the coupling between methyl groups. For the smallest molecules, comparison between the generalized semiempirical calculation and a limited ab initio calculation on dimers of molecules suggests the simple rotational model employed is adequate, and that discrepancies between measured and calculated values are due to incorrect modeling of the atom–atom potentials. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474527
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  • 4
    Electronic Resource
    Electronic Resource
    Rotational dynamics of methyl groups in durene: A crystallographic, spectroscopic, and molecular mechanics investigation (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 516-527 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Neutron powder diffraction measurements of perdeutero durene in the temperature range from 1.5 K to 290 K have been performed. The lowest temperature structure is the starting point for calculations of the methyl group tunneling and librational dynamics. Ab initio methods and atom–atom potentials are used to determine rotational single particle and coupling potentials. Tunneling splittings and librational bands are calculated by numerical solution of Schrödinger's equation for a system of many coupled methyl groups. High-resolution inelastic neutron scattering measurements of methyl tunneling and molecular vibrations have been repeated, the tunneling results resolving an inconsistency with earlier NMR work. Quantum molecular dynamics provide a stringent test of the numerical methods and the data are ultimately well reproduced. These results are also discussed in the context of optical measurements of dye molecules in a host lattice of durene. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478137
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of growth conditions and annealing parameters on the near-infrared optical absorption of epitaxial magnetic garnet films (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 436-440 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Several series of epitaxial films of nominal pure and bismuth-, aluminum-substituted yttrium iron garnet are grown on [111]-oriented paramagnetic substrates from PbO-fluxed melts. The growth rate is varied systematically by changing the supercooling. The optical absorption at a wavelength of 1330 nm and the concentrations of the impurities Pb2+, Pb4+, Pt4+, Si4+, and Ca2+ are measured. The absorption shows a minimum at a certain growth rate vmin, which increases linearly with the saturation temperature of the melt. The minimum of the absorption constant reaches values below 0.3 cm−1. The as-grown films contain a surplus of four-valent impurities, the minimum concentration of which correlates with the minimum of the optical absorption. The absorption of samples with growth rates higher than vmin can be reduced considerably by annealing in hydrogen atmosphere at 430 °C for a few minutes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350674
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