New solid-state NMR methods for exciting and separating anisotropic interactions of spin I = 1 nuclei
Date:
Lecture / Seminar
Time: 09:30-10:30
Location: Perlman Chemical Sciences Building
Lecturer: Dr. Rihard Aleksis
Organizer: Clore Institute for High-Field Magnetic Resonance Imaging and Spectroscopy
Details: Department of Materials and Environmental Chemistry, Stockholm University
Abstract: Solid-state NMR has become an essential tool for structural characterisation of ... Read more Solid-state NMR has become an essential tool for structural characterisation of materials,
in particular systems with poor crystallinity and structural disorder. In recent years, a surge of
interest has been observed for the study of paramagnetic systems, in which the interaction between
nuclei and unpaired electrons allows to probe the electronic structure and properties of materials
more directly. However, simultaneously this interaction leads to very broad resonances, which are
dicult to acquire and interpret. While signi cant advancements in both NMR instrumentation
and methodology have paved the way for the study of spin I = 1=2 nuclei in these systems, still
many issues remain to be resolved for routine investigation of quadrupolar nuclei I > 1=2. Here we
focus on improving both the excitation of the broad resonances and the resolution in the spectra
of spin I = 1 nuclei. The latter problem is addressed by developing methods for separation of the
shift and the quadrupolar interactions. We introduce two new methods under static conditions,
which have the advantage over previous experiments of both suppressing spectral artefacts and
exhibiting a broader excitation bandwidth. Furthermore, we demonstrate for the rst time an
approach for separation of the anisotropic parts of the shift and quadrupolar interaction under
magic-angle spinning. Secondly, to achieve broadband excitation we develop a new theoretical
formalism for phase-modulated pulse sequences in rotating solids, which are applicable to nuclear
spins with anisotropic interactions substantially larger than the spinning frequency, under conditions
where the radio-frequency amplitude is smaller than or comparable to the spinning frequency. We
apply the framework to the excitation of double-quantum spectra of 14N and design new pulse
schemes with
-encoded properties. Finally, we employ the new sequences together with density
functional theory calculations to elucidate the electron and hydride ion conduction mechanisms in
barium titanium oxyhydride.Close abstract
