Proton diffusion, quasielastic neutron scattering

Inelastic and quasielastic neutron scattering have special advantages for studying certain of the motional properties of protonated or organic species within zeolites and related microporous materials. These advantages and various experimental methods are outlined, and illustrated by measurements of torsional vibrations and rotational diffusion of tetramethylammonium (TMA) cations occluded within zeolites TMA-sodalite, omega, ZK-4 and S APO-20. 

Broadly speaking, the aim of an incoherent neutron scattering study is to characterize the individual translational and rotational diffusive motions of the scatterer (in this case, the proton held by an ion or molecule) at small energy transfers in the so-called quasielastic neutron scattering (QNS) region and the quantized vibrations at higher energy transfers in... 

Quasielastic neutron scattering (QENS) is a rather indirect method with many limitations. It makes use of the small ( quasielastic ) energy shift that neutrons experience in any scattering by a moving particle, say by the diffusive translations of protons on a molecule. Mathematically, the normalized scattered neutron intensity as a function of kinetic neutron energy E (or frequency (o=2nElh) is related to the time Fourier transform of the dynamic pair-distribution function G(r, i) of the sample material [6, 32]. Hence in Pick s approxima-... 

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