• E. R. deAzevedo, K. Saalwächter., O. Pascui, A. A. de Souza, T. J. Bonagamba, D. Reichert.
  Intermediate Motions as Studied by Solid-State SLF-NMR Experiments.
  J. Chem. Phys. 128, 104505 (2008). DOI 10.1063/1.2831798.

  Abstract

  In this report, the application of a class of separated-local field (SLF) NMR experiments named DIPSHIFT for probing motions in the intermediate regime is discussed. Simple analytical procedures based on the Anderson and Weiss (A-W) approximation are presented. In order to establish limits of validity of the A-W based formulas a comparison with spin dynamics simulations based on the solution of the stochastic Liouville-von-Neunmann equation is presented. It is shown that at short evolution times (less than 30% of the rotor period) the A-W based formulas are suitable for fitting the DIPSHIFT curves and extract kinetic parameters even in the case of jump like motions. However, full spin dynamics simulations provide a more reliable treatment and extend the frequency range of the molecular motions accessible by DIPSHIFT experiments. The decrease of the Cross-Polarization intensity due to the presence of intermediate regime molecular motions is also discussed, including spin dynamics simulations, which are used for the first time to establish the condition for minimal intensity loss. As an experimental test, molecular jumps of imidazol methyl sulfonate and trimethylsulfoxonium iodide (TMSI), as well as the side-chain motions in the photoluminescent polymer MEH-PPV were characterized. Possible extensions are also discussed.

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