Multiple quantum NMR spectroscopy onI> 1 nuclei in anisotropic systems

Abstract

The response of half-integral spin I > 1 nuclei in anisotropic systems to pulse sequences exciting multiple quantum (MQ) coherences is investigated theoretically. Using the state multipole formalism, we calculate the 2-dimensional (2D) MQ spectrum obtained by the conventional three-pulse sequence and compare it to recent experimental results. Next we consider MQ filters for detecting the evolution of rank (21 -1) single quantum coherences. Pulse sequences based on these filters can be used for revealing hidden anisotropy in a spectrum or for suppressing a dominant isotropic contribution. Finally, we develop 2D spinecho and quadrupolar echo experiments that refocus the inhomogeneous decay of various MQ coherences. These MQ echo techniques can be used to determine accurately the homogeneous line widths of various MQ transitions, as demonstrated by experimental results (including the first MQ quadrupolar echo spectra) on 23Na and 170 nuclei in a lyotropic liquid crystal.

Multiple-Time Correlation Functions in Spin-3/2 Solid-State NMR Spectroscopy

“…The quadrupolar precession functions g lЈl (m) ( Q t) (with ͉m͉ Յ l and lЈ) corresponding to this unitary transformation have also been presented by numerous authors in various forms (8,9,11,23,25,26,30,31,33,34). For convenience, in Table 1 we reproduce the SQ and DQ modulation factors (in the absence of relaxation effects) as the symmetric matrices g (ϩ1) and g (ϩ2) .…”

“…In an experimental study of the dynamic heterogeneity of a deuterated supercooled liquid the short t p limit of Eq. [9], i.e., a correlation function of the type ͗ 1 2 3 4 ͘, was explored as well (45). For I ϭ 3/ 2 nuclei it is also possible to access E 4 .…”

“…Consequently, to accomplish the succession of modulations as shown in Eq. [9] we need to choose coherence pathways such that during t m1 and t m3 even rank (i.e., quadrupolar) ordered and during t m2 odd rank (i.e., either Zeeman or octupolar) ordered states carry the desired quadrupolar modulations. )] (which cannot be converted into a simple expression via a baseline correction) will, however, not be considered further in the present article.…”

“…This then calls for the application of magic angle spinning and often, due to the low abundance of 6 Li, for isotopic enrichment. For 7 Li and 9 Be probes in solids the quadrupolar coupling is usually by far the strongest. Consequently, for the solid-state stimulated echo experiments mentioned above (6, 7) sample rotation techniques were not found to be necessary.…”

“…For solid materials in which only first-order quadrupolar perturbations are relevant, one may apply stimulated echo techniques for a detection of translational motions directly in the ultraslow regime. The first such applications employing spin-3/2 nuclei in solids include a study of the 9 Be dynamics in metallic glasses (6) and the investigation of the 7 Li jump processes in crystalline ion conductors (7). In both experiments the Jeener-Broekaert echo was recorded as a function of the mixing time, t m .…”