Protons, 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. 

Proton transfer mechanisms rely on several, generally slow, dynamical events. They are much studied at ambient temperatures in the case of biological samples but high temperatures are needed to obtain significant conduction from crystalline solids. These studies often rely on quasielastic neutron scattering techniques that are not discussed in this book, but see [47]. However, at low temperatures INS spectroscopy can provide direct information on the potential surface that controls the fast step, where the hydrogen atom transfers from the donor well to the acceptor well. 

The polymorphism of hydrogen sulfides of alkali metals M+(HS ) with M — Na, K, Rb, Cs was studied with neutron and X-ray diffraction, quasielastic neutron scattering, DSC and proton NMR. These compounds have three polymorphs and two known phase transitions. When M — Na, K, Rb, the LTP is monoclinic, the medium-temperature phase (MTP) is rho-mbohedral and the HTP is cubic with a NaCl-type structure. Owing to the fact that the sequence of phase transitions is the same for the three cations, this series is expected to be a model where coulombic interaction is modulated by the cation radii, which increases in the order Na, K, Rb, Cs. 

NMR and quasielastic neutron scattering (QNS) studies have been performed on PEO, O.42H3PO4 and PEO, O.66H3PO4 to investigate the phosphorus and proton dynamics in these systems . The temperature dependence of the conductivity is shown to be governed by the segmental... 

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... 

Fig. 6.8. Results of a quasielastic neutron scattering experiment on a melt of poly (ethylene-co-propylene) at 199 °C (10% protonated chains dissolved in a deuter-ated matrix M = 8.6 10 ) Intermediate scattering laws measured at the indicated scattering vectors top)] data representation using the dimensionless variable u = q 12kTa t/( ji) bottom). Prom Richter et al.[67]...

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-... 

The magnetic interaction of neutrons with protons or deuterons of the CH3 (CD3) group leads to the appearance of peaks of quasielastic and inelastic scattering, corresponding to AE and EaEb... 

---