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  • American Institute of Physics (AIP)  (32)
  • American Chemical Society (ACS)  (8)
  • 1
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    Water uptake profile in a model ion-exchange membrane: Conditions for water-rich channels (2015)
    American Institute of Physics (AIP)
    Details
    Publication Date: 2015-03-20
    Description: Ionic conductivity in a polymeric fuel cell requires water uptake. Previous theoretical studies of water uptake used idealized parameters. We report a parameter-free prediction of the water-swelling behavior of a model fuel cell membrane. The model polymers, poly(methyl-butylene)-block-poly(vinylbenzyl-trimethylamine), form lamellar domains that absorb water in humid air. We use the Scheutjens-Fleer methodology to predict the resulting change in lamellar structure and compare with x-ray scattering. The results suggest locally uniform water distributions. However, under conditions where a PVBTMA and water mixture phase-separate, the two phases arrange into stripes with a dilute stripe sandwiched between two concentrated stripes. A small amount of water enhances conductivity most when it is partitioned into such channels, improving fuel-cell performance.
    Print ISSN: 0021-9606
    Electronic ISSN: 1089-7690
    Topics: Chemistry and Pharmacology , Physics
    Published by American Institute of Physics (AIP)
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  • 2
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    Interplay Between Hydroxyl Density and Relaxations in Poly(vinylbenzyltrimethylammonium)-b-poly(methylbutylene) Membranes for Electrochemical Applications (2018)
    American Chemical Society (ACS)
    Details
    Publication Date: 2018-01-24
    Description: Journal of the American Chemical Society DOI: 10.1021/jacs.7b10524
    Print ISSN: 0002-7863
    Electronic ISSN: 1520-5126
    Topics: Chemistry and Pharmacology
    Published by American Chemical Society (ACS)
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  • 3
    Electronic Resource
    Electronic Resource
    Inhomogeneous broadening of electronic spectra in organic model systems (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 1821-1829 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We studied the inhomogeneous broadening of the electronic transitions of the linear polyene octatetraene doped into mixed crystal matrices of various n-alkanes with added halogenated alkanes. The additional broadening caused by the halogenated alkane molecules can be described at low concentrations by a Lorentzian, whose width depends linearly on the concentration. The analysis of the experimental data showed that the main contribution to the additional inhomogeneous broadening in the investigated systems is not given by the electrostatic and dispersive interactions, but by the fluctuation of the nuclear coordinates of the chromophore. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475559
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  • 4
    Electronic Resource
    Electronic Resource
    Electronic states of linear polyenes: High resolution spectroscopy of cis- and trans-1,3,5,7,9-decapentaene (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 9586-9593 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: High resolution fluorescence, one-photon excitation and two-photon excitation spectra of cis- and trans-1,3,5,7,9,-decapentaene have been measured in n-alkane matrices at 4.2 K and vibronic progressions have been analyzed. Trans-decapentaene in decane occupies a centrosymmetric site and one-photon transition occurs via mixing with a low frequency promoting vibrational mode. Cis-decapentaene can occupy two different sites in the crystal lattice of heptane with comparable probabilities. Some vibrations associated with the cis-double bond are observed in the emission spectra of cis-decapentaene. The totally symmetric double bond stretch vibration has a higher frequency in the excited 2 1Ag state ((approximate)1790 cm−1) than in the ground 1 1Ag state ((approximate)1600 cm−1). The appearance of another double bond vibrational band around 1530 cm−1 in the excitation spectra of trans-decapentaene may be evidence of substantial mixing of normal vibrational modes in the first excited 2 1Ag electronic state. The two-photon excitation spectra of the 1 1Ag→2 1Ag electronic transition of trans-decapentaene in n-decane and n-heptane exhibit vibronic progressions based on overtones of the totally symmetric double bond stretch vibrational mode. Five overtones of this mode are observed in the region 24 700–33 000 cm−1 and the vibronic progression appears to be nearly harmonic. No other Ag electronic states with an appreciable two-photon cross section have been observed in the region below 40 000 cm−1. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476407
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  • 5
    Electronic Resource
    Electronic Resource
    Octatetraene m 1Ag states: Two-photon fluorescence excitation spectrum from 28 000 to 50 000 cm−1 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 9297-9303 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The 2-photon fluorescence excitation spectra of all-trans octatetraene in n-hexane and n-octane host crystals at 77 and 1.8 K have been recorded for the region 28 000 to 50 000 cm−1. Measurements of the dependence of emission signal on excitation intensity and fluorescence lifetimes contributed to the assignment of the observed features. On the basis of their frequencies, intensities, and solvent shift behaviors all of the bands are seen in the region 28 000 to 44 000 cm−1 are assigned to vibronic bands of the 1 1Ag–2 1Ag transition. The unusual temperature dependence of one excitation feature is consistent with a near degeneracy of singlet and triplet levels. Above 44 000 cm−1 there are four broadbands, two of which must be assigned to 0–0 transitions from the 1 1Ag ground state to higher lying m 1Ag states at 45 030 and 46 710 cm−1, respectively. The other two bands at 48 000 and 49 860 cm−1 could be either vibronic additions to the 0–0 band at 46 710 cm−1 or 0–0 bands for new m 1Ag states. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471675
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  • 6
    Electronic Resource
    Electronic Resource
    Measuring internal electric fields with atomic resolution (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7773-7781 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper describes a scheme for analyzing the effects of external electric field on the excitation energy of a conjugated probe molecule that is faithful to the actual microscopic situation and treats all aspects of the problem consistently. Structure is obtained from a molecular mechanics simulation, internal and local fields are calculated by classical electrostatics, and shifts in excitation energy are calculated by incorporating site energies into a simple π-electron model. An example calculation demonstrates the ability of this procedure to determine microscopic electric fields and molecular charge distributions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469030
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  • 7
    Electronic Resource
    Electronic Resource
    Experimental determination of conjugation lengths in long polyene chains (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 6248-6252 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Since the low energy absorption spectrum of a linear polyene is dominated by the strongly allowed 1 1Ag→1 1Bu transition (S0 to S2), it can be reconstructed for any chain length if the 0–0 band excitation energy, the band profile, and intensity are known. From this premise, this paper uses information developed in high resolution experiments on well-defined linear polyenes to extract the distribution of effective conjugation lengths from absorption spectra of solutions of long linear polyenes. These distributions are found to be dominated by short conjugation lengths. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470402
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  • 8
    Electronic Resource
    Electronic Resource
    High resolution spectroscopy of diphenyldecapentaene and diphenyldodecahexaene (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 2433-2437 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Fluorescence and fluorescence excitation spectra of single crystal and polycrystalline solutions of diphenyldecapentaene in n-decane and diphenyldodecahexaene in n-dodecane have been measured at 77 and 4.2 K. At 4.2 K the spectra are well resolved (FWHM bandwidths (approximately-equal-to)10 cm−1) and, for the principal site, the energy for the 2 1Ag(S1) to 1 1Ag(S0) origin band of diphenyldecapentaene in n-decane is 20 133.3 cm−1 and that of diphenyldodecahexaene in n-dodecane is 18 261.4 cm−1. Analysis of these data includes the determination of fluorescence decay rates and C–C and C=C vibrational frequencies in the ground and excited states.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453134
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  • 9
    Electronic Resource
    Electronic Resource
    Two-photon excitation spectroscopy and excited state decay kinetics of isolated diphenylbutadiene (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2186-2190 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the two-photon excitation spectrum and decay kinetics of the two-photon prepared states for diphenylbutadiene in a helium free jet. The spectrum is that of a symmetry allowed two-photon transition and is assigned using 17 harmonic fundamentals. A reexamination of the previously reported one-photon excitation spectrum allows the assignment of several additional u symmetry fundamentals of diphenylbutadiene's excited 1Ag state. Curves of intensity vs time for light detected at two times the wave number frequency of the laser minus a Stoke's shift of between 1000 and 9000 cm−1 show two components. One, due to two-photon resonance enhanced hyper-Raman scattering, reproduces the temporal profile of the exciting laser. The other, due to fluorescence from the excited 1Ag state, decays exponentially. The fluorescence lifetime decreases with increasing excitation frequency from 100 ns for 0–0 band excitation to 13 ns for excitation at 1235 cm−1 above the origin, consistent with the onset of a nonradiative decay channel previously observed for diphenylbutadiene in one-photon studies. Above this energy only hyper-Raman scattering is detected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449310
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  • 10
    Electronic Resource
    Electronic Resource
    Saturation kinetics of the S0 to S2 optical transition in isolated diphenylhexatrienef a@f ) (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2939-2941 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A three level kinetic model is fitted to fluorescence intensities measured as a function of excitation intensity for the S0 to S2 transition of isolated diphenylhexatriene. Parameters derived in the fit are coupled with experimental observations to bracket the rate of energy redistribution from S2 to vibrationally excited levels of S1 and S0 to between 1010 and 4×1012 s−1. The rate of excitation, which is directly proportional to oscillator strength, is precisely determined in the fit to be 3.7×108 s−1 per μJ at the peak of our 6 ns FWHM laser pulse.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448242
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