Nuclear magnetic resonance studies, rotation detection

Spectroscopic methods, such as FT-infrared (FTIR) and Raman spectroscopy detect changes in molecular vibrational characteristics in noncrystalline solid and supercooled liquid states. Various nuclear magnetic resonance (NMR) techniques and electron spin resonance (ESR) spectroscopy, however, are more commonly used, detecting transition-related changes in molecular rotation and diffusion (Champion et al. 2000). These methods have been used for studies of the amorphous state of a number of sugars in dehydrated and freeze-concentrated systems (Roudaut et al. 2004). 

Solid-state nuclear magnetic resonance (NMR) has been extensively used to assess structural properties, electronic parameters and diffusion behavior of the hydride phases of numerous metals and alloys using mostly transient NMR techniques or low-resolution spectroscopy [3]. The NMR relaxation times are extremely useful to assess various diffusion processes over very wide ranges of hydrogen mobility in crystalline and amorphous phases [3]. In addition, several borohydrides [4-6] and alanates [7-11] have also been characterized by these conventional solid-state NMR methods over the years where most attention was on rotation dynamics of the BHT, A1H4, and AlHe anions detection of order-disorder phase transitions or thermal decomposition. There has been little indication of fast long-range diffusion behavior in any complex hydride studied by NMR to date [4-11]. 

There are many experimental techniques for the determination of the Spin-Hamiltonian parameters g, Ux, J. D, E. Often applied are Electron Paramagnetic or Spin Resonance (EPR, ESR), Electron Nuclear Double Resonance (ENDOR) or Triple Resonance, Electron-Electron Double Resonance (ELDOR), Nuclear Magnetic Resonance (NMR), occasionally utilizing effects of Chemically Induced Dynamic Nuclear Polarization (CIDNP), Optical Detections of Magnetic Resonance (ODMR) or Microwave Optical Double Resonance (MODR), Laser Magnetic Resonance (LMR), Atomic Beam Spectroscopy, and Muon Spin Rotation (/iSR). The extraction of data from the spectra varies with the methods, the system studied and the physical state of the sample (gas, liquid, unordered or ordered solid). For these procedures the reader is referred to the monographs (D). Further, effective magnetic moments of free radicals are often obtained from static... 

Nuclear magnetic resonance and inelastic neutron scattering have both been used to study the local dynamical response of the ring motions in PANl [57,58] and in PPV films [59,60]. The NMR experiments are able to detect the two aforementioned types of motion, ring flips and librations. At lower temperatures the ring motion is almost exclusively librational with modest torsional excursions about an equilibrium position. At elevated temperatures there are pronounced flips, approaching a full 180° of rotation. 

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