Effect of Hydration on the Local Symmetry around Aluminum in ZSM-5 Zeolites Studied by Al-27 Nuclear Magnetic-Resonance

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Coherent Cross-Polarization Theory for a Spin-½ Coupled to a General Object

Zero-order average-Hamiltonian theory is used to extend the product-operator description of coherent spin–spin cross-polarization to the case of a spin-½ coupled to a general object, like a molecular rotor or a quantum oscillator. The object, which is not necessarily in a Boltzmann equilibrium state, is assumed to have no interaction with the lattice and no internal relaxation capacity. The Bloch–Wangsness–Redfield (BWR) theory for incoherent processes like spin–lattice relaxation does not apply for such an isolated spin– object pair. Nevertheless spectral density at the Larmor frequency, of key importance in BWR theory, also plays a central role in object-induced spin polarization. Spectral density in our theory is represented by quantum operators J2 and J1. If J2 and J1 do not commute, the spin– object coupling may cause spin polarization in an initially saturated spin system. This represents a coherent mechanism for spin cooling, which in specific cases may lead to enhanced spin polarization above the thermal equilibrium value. A master equation is derived for general spin– object crosspolarization, and applied to the case of a spin pair inside a uniaxial rotor, and a spin coupled to a microelectronic LC circuit

129Xe-NMR of carbon black filled elastomers

It is shown that 129Xe-NMR is a powerful tool to investigate carbon black and carbon black filled elastomers. For the carbon black material itself the129Xe chemical shift of xenon adsorbed at the surface of carbon black aggregates yields information about the relative average pore size of the carbon black aggregates. The experimental 129Xe-NMR results of carbon black filled ethylene-propylene-diene (EPDM) can be explained when it is assumed that the xenon atoms in the bound EPDM fraction exchange rapidly on the NMR time scale between a state where they are adsorbed on the carbon black surface and a state in which they are absorbed in the EPDM layer. This would imply that the carbon black aggregates are not completely covered with EPDM chains

Al-27 Nutation NMR of Zeolites

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Heteronuclear J-Resolved Solid-State NMR of Filled Natural-Rubber

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Ultraslow Molecular Motions in Crystalline Polyoxymethylene - a Complete Elucidation Using Two-Dimensional Solid-State NMR

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Proton Magic Angle Spinning Nuclear Magnetic-Resonance and Temperature Programmed Desorption Studies of Ammonia on the Acidity of the Framework Hydroxyl-Groups in the Zeolite H-ZSM-5 and in H-Boralite

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Two-Dimensional Exchange NMR in Rotating Solids - a Technique to Study Very Slow Molecular Reorientations

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