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