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  • 1
    Electronic Resource
    Electronic Resource
    High energy inelastic neutron scattering from physisorbed hydrogen in cesium intercalated graphite (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7153-7162 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The inelastic neutron scattering from H2 in C24Cs(H2)x has been measured at momentum transfers of 8〈Q〈22 A(ring)−1 as a function of filling, 0.5〈x〈2.0, and temperature from 20 to 150 K. The observed scattering approaches the limiting behavior predicted by the Impulse Approximation (IA) for molecular hydrogen for Q's greater than 15 A(ring)−1 and is insensitive to the filling factor and temperature up to kT/M≈0.1, where M is the enthalpy of hydrogen sorption. The results are analyzed using a model for the IA scattering from molecular hydrogen which takes into account the excitation of rotational transitions and the presence of a local orientational potential at the hydrogen adsorption sites. The average translational kinetic energy per molecule, which is determined by the effective local potential for the molecule, can be extracted from the measured scattering. For a powder sample, such as used in this measurement, determination of the kinetic energy requires independent knowledge of the orientational potential of the H2 molecules. Using the orientational potential inferred from previous tunneling measurements we extract an average translation kinetic energy of 320 K for the H2 molecule in the intercalate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459439
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  • 2
    Electronic Resource
    Electronic Resource
    Freezing in confined geometries (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 777-779 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results of detailed structural studies, using elastic neutron scattering, of the freezing of liquid O2 and D2 in porous vycor glass are presented. The experimental studies have been complemented by computer simulations of the dynamics of freezing of a Lennard-Jones liquid in narrow channels bounded by molecular walls. Our results point to a new simple physical interpretation of freezing in confined geometries.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108461
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  • 3
    Electronic Resource
    Electronic Resource
    Microscopic origins of superfluidity in confined geometries (1996)
    [s.l.] : Nature Publishing Group
    Nature 379 (1996), S. 616-618 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The exact nature of the confining medium determines the type of disorder and its effects, on the transition. For example, the superfluid transition of helium confined in vycor glass which has a compact structure with well defined small ( 70-A) pores, is considerably suppressed, but still has ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/379616a0
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  • 4
    Electronic Resource
    Electronic Resource
    Density and temperature dependence of the momentum distribution in liquid helium 4 (1995)
    Springer
    Journal of low temperature physics 101 (1995), S. 881-928 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Deep inelastic neutron scattering measurements on liquid4He have been carried out for temperatures from 0.35 K to 4.2 K and densities from 0.125 to 0.200g/cm3 at a momentum transfer of 23 Å−1. These measurements are at large enough momentum transfer that deviations from the Impulse Approximation are accurately described by current theories and information on the single particle momentum distribution may be extracted from the measured scattering. The scattering exhibits non-Gausian behavior in both the normal liquid and superfluid phases. A distinct change in the scattering, marked by a reduction in the width and increased deviations from the classical Gaussian shape, occurs at the suerfluid transition. We present a comparison of our experimental results with recent calculations at a variety of temperatures and densities and show that theory and experiment are in excellent agreement. We also present model scattering functions, obtained by correcting for instrumental resolution and final state effects, that represent the scattering in the IA limit. Finally, we present values for the average kinetic energy and the Bose condensate fraction over a broad range densities and temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754515
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  • 5
    Electronic Resource
    Electronic Resource
    A Quasi-Elastic and Inelastic Neutron Scattering Study of H2 in Zeolite (1999)
    Springer
    Journal of low temperature physics 116 (1999), S. 149-165 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The diffusion of molecular hydrogen adsorbed in zeolite 13X at high coverage's has been studied by quasi-elastic neutron scattering for temperatures ranging from 0 to 60 K. No diffusive motion was observed, within instrumental resolution, at temperatures below 20 K, well above the bulk melting point of H 2 , in contrast to recent NMR studies. The diffusive motion of the adsorbed H 2 could be described by a liquid like jump diffusion model above 35 K. The diffusion coefficient demonstrates an Arrhenius behavior: D = D0 exp(E/kT), with D0 = 1.2 × 10 −8 m 2 /s and an activation energy of E = 62 K. The inelastic scattering spectrum has also been studied. The scattering consisted of several peaks superimposed on a broad background extending from 1 meV to above 100 meV and is consistent with rotational transitions for a hindered rotor in a strong orientational potential with a broad distribution of barrier heights.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021881516198
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  • 6
    Electronic Resource
    Electronic Resource
    The momentum distribution of liquid hydrogen in vycor (1991)
    Springer
    Journal of low temperature physics 83 (1991), S. 165-175 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Deep inelastic neutron scattering (DINS) measurements of molecular hydrogen adsorbed in porous vycor glass at 18 K have been carried out for pore fillings ranging from sub-monolayer coverage to nearly full pore. DINS provides direct information on the momentum distribution of hydrogen in the vycor that, due to the light mass of the hydrogen molecule, is determined by the local environment of the molecule. The observed scattering is consistent with the impulse approximation (IA) using a model in which the hydrogen molecules behave as free rotors that are decoupled from the translational motion. The translational kinetic energy is 95 K for monolayer coverage, reflecting the binding of the molecules to the surface, and decreases, as the pore filling is increased, to 73 K for the nearly full pore case.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00682116
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  • 7
    Electronic Resource
    Electronic Resource
    Deep inelastic neutron scattering from liquid4He in aerogel glass (1990)
    Springer
    Journal of low temperature physics 80 (1990), S. 197-220 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report highQ inelastic neutron scattering studies of liquid4He confined inside porous aerogel glass in both the normal and superfluid phases. The scattering consists of a broad component, which we interpret as due to atoms localized on the surface of the glass, and a narrow component, which we interpret as due to the confined liquid inside the pores. The broad component is quite small, and no quantitative analysis is attempted. However, the narrow component due to the confined liquid is sufficiently large that information on the kinetic energy and condensate fraction may be obtained. The measurements are at large enoughQ (23 Å−1) that the incoherent approximation may be used to directly extract the kinetic energy. Furthermore, the observed scattering is consistent with the impulse approximation, allowing information on both the momentum distribution and the condensate fraction to be extracted. The kinetic energy of the confined liquid is close to previous measurements of the kinetic energy in the bulk liquid. The condensate fraction of the confined liquid, which is estimated using a modification of a method due to Sears, is close to previous estimates of the condensate fraction in the bulk liquid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00683486
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  • 8
    Electronic Resource
    Electronic Resource
    Symposium on Quantum Fluids and Solids (1992)
    Springer
    Journal of low temperature physics 89 (1992), S. 1-3 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00692572
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  • 9
    Electronic Resource
    Electronic Resource
    The structure of deuterium in vycor (1995)
    Springer
    Journal of low temperature physics 101 (1995), S. 929-949 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutron diffraction studies of normal deuterium in porous vycor glass have been carried out at temperatures in the range 4 to 20 K as a function of pore filling. For pore fillings, f, above f = 0.6 we find that the D2 in the pores forms a crystalline solid with a large amorphous component. The appearance of the crystalline phase is characterized by supercooling and hysteresis of the liquid-solid transition in agreement with previous thermodynamic studies. The crystalline phase has a structure which is different from the bulk and exhibits a large correlation length. Pore fillings below f = 0.6 show no sign of crystalline ordering, although enhanced short range ordering is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754516
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  • 10
    Electronic Resource
    Electronic Resource
    A neutron scattering study of hydrogen in vycor glass (1996)
    Springer
    Journal of low temperature physics 103 (1996), S. 23-33 
    Details
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The elastic, quasi-elastic, and deep inelastic scattering of para-hydrogen in porous vycor glass have been measured in both the solid and liquid phase. At temperatures above 12 K, the H2 in the pores can be described as a bulk-like liquid with a single tightly bound layer at the pore surface. At temperatures below 8 K, the hydrogen in the pores is solidified into a crystalline structure different from that of the bulk. No indication of migration of the hydrogen out of the pores as recently proposed to explain torsional oscillator measurements, is observed. The momentum distribution of the hydrogen in the pores at both low and high temperatures is Gaussian and shows no indication of a Base condensate peak.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00754655
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