School of Chemistry, Faculty of Exact sciences
Nuclear magnetic resonance characterization of polarization, coherence, structure and lifetimes of atoms with extensively large anisotropic spin interactions
The phenomena of magnetic resonance is best described by the quantum Zeeman effect, which is perturbed to first and second order by internal spin interactions. It provide atomic-resolution information on structure and dynamics for a wide-range of materials, many of which must be studied in the solid and semi-solid state. Under such conditions the technique of magic-angle spinning nuclear magnetic resonance (MAS NMR) is highly useful; however, it introduces two complications: spin interactions become orientation dependent (anisotropy) and time dependent. Thus, it requires us to be able to excite a broad range of frequencies, often spanning more than our available excitation bandwidth, and we are obliged to solve the time-dependent Liouville von Neumann equations of motion.
Our research focuses on the development, theory, and application of NMR techniques to study atoms that possess very large anisotropic interactions (namely the quadrupolar interaction and chemical shift anisotropy). Those atoms account for the majority of elements in the periodic table and exist in most materials of interest. Example are metals, metal ions, halogens, oxygen and nitrogen etc. Consequently, the applicability of our techniques are of broad interest to a variety of chemical disciplines including metalloenzymes, metal-based catalysts, halogenated materials and many more.
In one of our main developmental achievements, we managed to device and describe a technique that can uniformly saturate a very broad range of frequencies by utilizing a unique phase shaping of the radio-frequency NMR pulses. Consequently we managed to show how accurate inter-atomic distances can be measured to very high precision (0.01 nm) when one of the atoms has an extensively large anisotropy, and using the same approach we can now probe accurate lifetimes of such spins. This result has implications to the study of semi-conducting and super-conducting materials.