Zhou J, Li L, Hu H, Yang B, Dan Z, Qiu J, Guo J, Chen F, Ye C
Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Institute of Physics, Chinese Academy of Sciences, Wuhan.
Solid State Nucl Magn Reson. 1994 Nov;3(6):339-51. doi: 10.1016/0926-2040(94)90018-3.
The results of a study of two types of natural-diamond crystals by dynamic nuclear polarization (DNP)-enhanced high-resolution solid-state 13C nuclear magnetic resonance (NMR) are reported. The home-built DNP magic-angle spinning (MAS) 13C NMR spectrometer operates at 54 GHz for electrons and 20.2 MHz for carbons. The power of the microwave source was about 30 W and the highest DNP enhancement factor came near to 10(3). It was shown that in the MAS spectra the 13C NMR linewidths of the Ib-type diamond were broader than those of IaB3-type diamond. From the hyperfine structure of the DNP enhancement as a function of frequency, four kinds of nitrogen-centred and one kind of carbon-centred free radicals could be identified in the Ib-type diamond. The hyperfine structures of the DNP enhancement curve that originated from the anisotropic hyperfine interaction between electron and nuclei could be partially averaged out by MAS. The 13C polarization time of DNP was rather long, i.e. 1500 s, and the spin-lattice relaxation time (without microwave irradiation) was about 300 s, which was somewhat shorter than anticipated. Discussions on these experimental results have been made in this report.
报道了通过动态核极化（DNP）增强的高分辨率固态13C核磁共振（NMR）对两种天然金刚石晶体的研究结果。自行搭建的DNP魔角旋转（MAS）13C NMR光谱仪，电子工作频率为54 GHz，碳的工作频率为20.2 MHz。微波源功率约为30 W，最高DNP增强因子接近10³。结果表明，在MAS光谱中，Ib型金刚石的13C NMR线宽比IaB3型金刚石的宽。根据DNP增强的超精细结构随频率的变化，在Ib型金刚石中可识别出四种以氮为中心和一种以碳为中心的自由基。源于电子与原子核之间各向异性超精细相互作用的DNP增强曲线的超精细结构可通过MAS部分平均化。DNP的13C极化时间相当长，即1500 s，自旋晶格弛豫时间（无微波辐射）约为300 s，比预期略短。本报告对这些实验结果进行了讨论。
