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  • Articles  (37,958)
  • American Institute of Physics (AIP)  (31,708)
  • American Physical Society (APS)
  • International Union of Crystallography (IUCr)
  • 1985-1989  (37,958)
Collection
  • Articles  (37,958)
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  • 11
    Electronic Resource
    Electronic Resource
    Dissociation energy of the molecule AlBr from equilibrium measurements (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4909-4911 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociation equilibrium AlBr=Al+Br was studied by effusion beam mass spectrometry over the range 1970 to 2260 K and the dissociation energy D00(AlBr) was derived as 4.41±0.06 eV. This value is in general agreement with other fragmentary thermochemical results, but it is lower than a value derived from a short extrapolation of vibrational levels in the excited 1π state, doubtless because of a potential maximum of about 0.22 eV in that state. A Birge–Sponer extrapolation of the ground state vibrational levels, when corrected for degree of ionicity, yields a D00 value in close accord with the experimental result, but an electrostatic model calculation falls short by 0.45 eV.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456730
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  • 12
    Electronic Resource
    Electronic Resource
    A new scheme for determination of the carrier mobility and main-chain conformation of an electroactive polymer chain by transient electric birefringence (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4920-4925 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A new scheme of experimental criterion is proposed for estimating the carrier mobility and main-chain conformation of an electroactive polymer chain by the technique of transient electric birefringence (TEB). The rise response Δnr (t) and the decay response Δnd (t) in the TEB satisfy in the Kerr regime (i) Δnr (t)=Δnst -Δnd (t) for a polymer molecule of arbitrary conformation with an induced dipole moment alone arising from carriers highly mobile along the main chain, (ii) Δnr (t)=Δnst -(3/2)Δnd (t/3)+(1/2)Δnd (t) for a rodlike polymer molecule with a permanent dipole moment alone originating from carriers with low mobility, and (iii) Δnr(t)=Δnst-2Δnd (t/2)+Δnd (t) for a random-coiled polymer with a permanent dipole moment alone due to low-mobility carriers, where Δnst =limt→∞ Δnr(t) . Then, comparison of the TEB rise and decay responses gives us information on the carrier mobility and main-chain conformation. This criterion is valid also for polydispersed polymer samples. By applying the criterion to the exemplifying data of the TEB responses for soluble urethane-substituted polydiacetylenes, it is found that the polydiacetylene molecules take a random-coil conformation with a permanent dipole moment in a good solvent, while in a poor solvent the carrier mobility depends crucially on the solvent condition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456732
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  • 13
    Electronic Resource
    Electronic Resource
    Imaging of spatial pattern formation in an oscillatory surface reaction by scanning photoemission microscopy (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4942-4948 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The rate of catalytic carbon monoxide oxidation on a Pt(100) single crystal surface under isothermal, low-pressure conditions exhibits for certain ranges of parameters (O2 and CO partial pressures, temperature) sustained temporal oscillations whose mechanism had been explored in previous work. Coupling between reaction and diffusion leads to spatial pattern formation as manifested by patches with different work function on the intrinsically homogeneous surface. Imaging is performed by means of the novel technique of scanning photoemission microscopy. Typically, nuclei with dimensions of a few microns, as determined by the instrumental resolution, are formed spontaneously and expand with sharp fronts and velocities of about 0.5 mm/min (at 480 K) up to sizes ≥1 mm. Waves with even more extended fronts propagating with somewhat higher velocities across the sample surface are responsible for the occurrence of large amplitude temporal oscillations of the integral reaction rate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456735
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  • 14
    Electronic Resource
    Electronic Resource
    The bonding of acetonitrile and CH2CN on Ag(110) determined by near edge x-ray absorption fine structure: Evidence for π-donor bonding and azimuthal ordering (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4338-4345 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Carbon K edge near edge x-ray absorption fine structure (NEXAFS) spectra of adsorbed acetonitrile and reactive intermediates derived therefrom on Ag(110) were studied in order to determine their orientation and bonding to the surface. For both the multilayer and the adsorbed monolayer there is excellent agreement between the spectra of the adsorbed acetonitrile and the gas phase species. For the multilayer coverage the orientation of the acetonitrile molecules is not completely random; the molecules prefer an orientation with their bond axes closer to parallel than perpendicular to the surface. At monolayer coverage acetonitrile bound to the surface is unrehybridized. It is bound with its linear molecular skeleton parallel to the surface and randomly oriented azimuthally. Annealing molecular CH3 CN to 325 K in the presence of coadsorbed atomic oxygen produces a linear CH2 CN surface intermediate, the molecular axis of which is parallel to the surface and perpendicular to the close-packed direction. The C–C and C–N bond lengths are essentially unperturbed from their values in gas phase CH3 CN. Bonding appears to occur between the methylene carbon and the metal, as expected. A broadening of the π* resonance for transition into the π* orbital perpendicular to the surface is interpreted in terms of π-donor bonding.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456814
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  • 15
    Electronic Resource
    Electronic Resource
    Attenuated total reflectance infrared spectra of strongly absorbing anisotropic crystals: Orthorhombic Na2[Fe(CN)5NO]⋅2H2O (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4265-4272 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Attenuated total reflectance (ATR) from principal faces of orthorhombic (and higher symmetry) crystals in spectral regions including strongly polar optic modes is considered. A detailed, quantitative comparison between experimental and calculated ATR infrared (IR) spectra of orthorhombic sodium nitroprusside dihydrate (SNP), Na2[Fe(CN)5NO]⋅2H2O, single crystals in the 500–3800 cm−1 region is presented. Calculated ATR spectra are generated employing the dielectric tensor of SNP obtained from Kramers–Kronig analysis of external reflectance data. The dependence of intensities, profiles, and locations of bands in the spectra upon the relative refractive index of the sample against the ATR prism and the polarization state of the reflected IR beam will be discussed. Both theoretical and experimental evidence of the coupling of the TM-polarized evanescent wave with strong in-plane-polarized optic modes at about their LO frequencies will be given with reference to the case of the strong NO stretching mode of SNP. Finally, the computed and experimental ATR results in SNP single crystals will be critically compared with powder ATR data and reported polarized IR transmittance spectra of SNP single crystals plates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456806
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  • 16
    Electronic Resource
    Electronic Resource
    X-ray diffraction study of liquid n-butane at 140 and 267 K (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4299-4306 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: X-ray diffraction data for liquid n-butane near the triple and boiling points are presented. The data are analyzed using scattering factors for −CH3 and −CH2 groups which permits extraction of structure and distribution functions for carbon sites. An intramolecular carbon–carbon distance at approximately 3.1 A(ring) is assigned to a short end-to-end distance in a near-gauche conformation, which is in agreement with the electron diffraction results for gaseous n-butane. The intermolecular pair distribution functions show a large difference in the liquid structure for the low and high temperature states, similar to that found in liquid propane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456810
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  • 17
    Electronic Resource
    Electronic Resource
    Kinetics of the thermal desorption of indium from GaAs(100) (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4330-4337 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report studies of the kinetics of thermal desorption of In from Ga-stabilized GaAs(100) in ultrahigh vacuum. The relative coverage of In was monitored by x-ray photoelectron spectroscopy (XPS), while the substrate temperature was accurately measured using infrared laser interferometric thermometry. The In was deposited on GaAs by dosing, at room temperature, to saturated monolayer coverage with trimethylindium, yielding In ∼2×1014 cm−2. Subsequent heating to 400 °C desorbs all hydrocarbon species without affecting the In coverage. Further heating leads to first-order desorption of In, as confirmed by exponential decay of In(3d 5/2) XPS signal in isothermal desorption experiments at 473 and 503 °C. From temperature programmed desorption studies through the range 450 to 530 °C, differentiation of the In coverage vs time yielded desorption rates from which Arrhenius parameters were extracted. The unit-weighted average values of the preexponential factor and the desorption energy, obtained from three experiments with heating rates from 0.6 to 3.2 °C/min, are: log10A(s−1)=12.2±0.5 and Ed=53.5±1.2 kcal/mol, where the uncertainties are 1σ sample standard deviations. The Arrhenius parameters of desorption of In from Ga-stabilized GaAs(100) are found to be similar to those of vaporization of pure In. This is consistent with the known tendency of In to form islands on GaAs surfaces, but could also reflect the similarity of the local environments of an In atom adsorbed on an In island and an In atom adsorbed on a Ga-terminated surface. The observed first-order kinetics and the constancy of the In(3d 5/2) XPS signal up to the temperature where desorption occurs indicates that if islands are formed they are small (〈10 A(ring) diameter) at the low coverage used here.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456813
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  • 18
    Electronic Resource
    Electronic Resource
    Quasielastic light scattering studies of swollen and stretched polymer gels (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4360-4368 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Cooperative diffusion D of polyacrylamide gels in water was investigated by quasielastic light scattering both under the isotropically swollen state and under the uniaxially stretched and swollen state. The concentration (Ce) dependence of D for the isotropic gels having equilibrium degrees of swelling was measured by systematically changing crosslinking density of gels. The results yielded D=(3.4±0.5)×10−6 C0.76±0.03e cm2/s, in accord with a scaling prediction. For each of the gels prepared and having a given Ce, the uniaxial stretching was applied, and the values D were investigated as a function of extension ratio α and direction β with respect to the stretching direction. The results gave D (α,Ce)=(3.4±0.5)×10−6 αx Cye cm2/s, where x=2/3 for β=0° and −1/4 for β=90°, and y=0.76, independent of α and β. The results clearly indicate that upon increasing α, D increases and decreases, respectively, in the direction parallel and perpendicular to the stretching direction, implying suppression and enhancement of the concentration fluctuations as a result of the network being stiffened and softened in the respective directions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457638
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  • 19
    Electronic Resource
    Electronic Resource
    Leading concentration correction to polymer dynamic self-structure factor (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4387-4400 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The discrete chain representation of multiple scattering theory of the concentration dependence of the hydrodynamics of polymer solutions is applied to the calculation of the leading concentration correction to the dynamic structure factor S(k,t) and its first and second cumulants of individual labeled Gaussian chains in theta solutions at nonzero concentrations. Contributions are separated into those from overall translational and internal chain motions as well as couplings between different internal modes and between translation and internal modes, coupling that are introduced by interchain hydrodynamic interactions. The separate contributions are analyzed as a function of k and of t in order to isolate regions where certain contributions are dominant. As expected, short times and larger k tend to favor contributions from internal chain dynamics, while longer times and smaller k make concentration dependent translational effects predominate. Computations for shorter chains are extrapolated to provide the asymptotic long chain behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457636
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  • 20
    Electronic Resource
    Electronic Resource
    Symmetry breaking in HCl and DCl dimers: A direct near-infrared measurement of interconversion tunneling rates (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 4418-4419 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The interconversion tunneling frequencies for (HCl)2 and (DCl)2 are obtained from near-infrared absorption spectra of the H(D)Cl stretching transitions, to spectroscopic precision for the mixed 35Cl–37Cl dimers. A phenomenological model of the interconversion process explains several experimental observations, and provides good estimates of the splittings expected for the 35Cl–35Cl and 37Cl–37Cl species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456774
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