| dc.description.abstract | The phenomenon of Nuclear Spin Optical Rotation (NSOR) is a member of the
nuclear magneto-optic effects. This is a spectroscopic phenomenon based on observing
the polarization state of a light beam after it interacts with nuclei of non-zero spin
magnetization. The NSOR effect relies on the hyperfine interactions between nuclear
spins and electrons. Therefore, it provides the ability to extract information on electronic
states at the specific nuclear sites of the molecules in samples. The most critical
challenge of the NSOR experiment is its intrinsic low signal-to-noise ratio (SNR). The
most straightforward way of solving this problem is to increase the polarization level
of nuclear spins. In this work, by using the dissolution dynamic nuclear polarization
(DNP) technique, the polarization level is increased by the order of 10⁴ compared to the
polarization obtained in a superconducting magnet. This increase can potentially solve the
low SNR problem.
A low field NMR instrument was constructed for observing NSOR in conjunction with
a dynamic nuclear polarizer. Longitudinal relaxation rates of four different concentrations
of radicals were determined, and paramagnetic relaxation enhancement was quantified.
The concentration of radical affected the polarization level inside the DNP polarizer and
the loss during sample transfer. An optimal concentration was found to be 30 mM, which
resulted in a 5 % polarization level after optimizing the injection time. This polarization
level was determined to be sufficient for a single scan NSOR experiment.
NSOR signals were then obtained with a circulation system by prepolarizing the
sample inside a superconducting magnet. Multi-nuclear NSOR measurement and
frequency-resolved NSOR at the low field were demonstrated for the first time. In a sample of 1:1 trifluoroethanol (TFE), water mixture containing ¹⁹F and ¹H NSOR signals
were simultaneously obtained, and the fluorine NSOR constant was determined to be 46
times larger than the proton. Triplet fluorine NSOR signal was observed due to spin-spin
interactions.
Finally, NSOR signals of proton and fluorine were obtained with the dissolution DNP
technique. A bubble trap and a focusing lens system minimized the negative effects of
gas bubbles and variations of the refractive index of the injected DNP sample, without
which the optical signal strength would be reduced. The NSOR signal was for the first
time observed in a single scan, with SNR of over 6. The signal from a more than 100-fold
diluted DNP sample is over 30 times larger than the signal obtained with a pure sample
prepolarized by a superconducting magnet. Further optimization of sample cell geometry
with the help of flow dynamics could lead to even higher SNR. With such increased SNR,
the NSOR effect can potentially be applied for a hybrid optical-NMR spectroscopy, which
can be used to study the local electronic excitation around a specific nucleus. | en |
