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Accurate knowledge of the rubidium (Rb) vapor density, , is necessary to correctly model the spin dynamics of Xe-Rb spin-exchange optical pumping (SEOP). Here we present a systematic evaluation of within a high-throughput Xe-Rb hyperpolarizer during continuous-flow SEOP. Near-infrared ( (D)/5 (D)) and violet (/6) atomic absorption spectroscopy was used to measure within 3.5 L cylindrical SEOP cells containing different spatial distributions and amounts of Rb metal. We were able to quantify deviation from the Beer-Lambert law at high optical depth for D and 6 absorption by comparison with measurements of the D and 6 absorption lines, respectively. D absorption deviates from the Beer-Lambert law at m whilst 5S absorption deviates from the Beer-Lambert law at m. The measured was used to estimate a Xe-Rb spin exchange cross section of m s, consistent with spin-exchange cross sections from the literature. Significant heterogeneity was observed in a SEOP cell containing 1 g of Rb localized at the back of the cell. While homogeneity was improved for a greater surface area of the Rb source distribution in the cell, or by using a Rb presaturator, the measured was consistently lower than that predicted by saturation Rb vapor density curves. Efforts to optimize and thermal management within spin polarizer systems are necessary to maximize potential future enhancements of this technology. 相似文献
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The NMR properties (chemical shift and spin-spin coupling constants) of (129)Xe in covalent compounds and weakly bound complexes have been investigated by DFT methods including relativistic effects. For covalent species, a good agreement between experimental and calculated results is achieved without scalar relativistic effects, but their inclusion (with a triple-zeta, double-polarization basis set) leads to some improvement in the quality of the correlation. The spin-orbit coupling term has a significant effect on the shielding constant, but makes a small contribution to the chemical shift. Coupling constants contain substantial contributions from the Fermi contact and paramagnetic spin-orbit terms; unlike light nuclei the spin-dipole term is also large, whereas the diamagnetic spin-orbit term is negligible. For van der Waals dimers, the dependence of the xenon chemical shift and anisotropy is calculated as a function of the distance. Small (<1 Hz) but non-negligible through-space coupling constants between (129)Xe and (13)C or (1)H are predicted. Much larger couplings, of the order of few Hz, are calculated between xenon and (17)O in a model silicate residue. 相似文献