CP/MAS of quadrupolar S=3/2 nuclei

被引:232
作者
Vega, Alexander J. [1 ]
机构
[1] Du Pont Cent Res & Dev, Expt Stn, Wilmington, DE 19880 USA
关键词
cross-polarization; quadrupolar nuclei; NMR spectroscopy;
D O I
10.1016/0926-2040(92)90006-U
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
The spin dynamics of Hartmann-Hahn cross-polarization from I = 1/2 to quadrupolar S = 3/2 nuclei is investigated. A density-matrix model applicable to cases where the quadrupole frequency v(q) is much larger than the rf amplitude v(1s) of the S spins, predicts the time development of the spin state of an isolated I, S spin pair in static situations and in three distinct cases of magic-angle-spinning speed v(R). These cases are characterized as slow, intermediate, and fast, depending on the magnitude of the parameter alpha = v(1s)(2)/v(q)v(R) relative to the intermediate value of 0.4. The model predictions are supported by numerical simulations. The polarization transfer from I to S is efficient in the limits of slow and fast sample spinning. When alpha << 1, the Hartmann-Hahn condition is shifted over once or twice v(R). When the spinning rate is intermediate, poor spin-locking of the quadrupolar spins prevents the accumulation of a cross-polarization signal and, in addition, depletes the spin-locked I magnetization. Experimental CP/MAS data obtained in NaOH show that the concepts developed for isolated spin pairs are also applicable to cross-polarization in a strongly coupled multi-spin system.
引用
收藏
页码:17 / 32
页数:16
相关论文
共 28 条