Nimerovsky E, Haimovich A, Goldbourt A
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv 69978, Tel Aviv, Israel.
School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv 69978, Tel Aviv, Israel.
Solid State Nucl Magn Reson. 2015 Nov;72:127-31. doi: 10.1016/j.ssnmr.2015.08.003. Epub 2015 Aug 21.
Distance measurements between a half-spin and a quadrupolar S=1 spin having a small quadrupolar coupling constant can be performed using the rotational echo double resonance (REDOR) experiment. We derived an analytical expression for the probability of transitions between energy levels resulting from the application of an arbitrary pulse flip angle to the quadrupolar spin and consequently minimized the probability that populations of individual levels do not undergo a spin transition during the pulse. As a result we discovered that if the flip angle of the quadrupolar spin pulse is 109.47°, the maximal recoupling values are the largest possible and the signal reaches a maximum value of 8/9, larger than in the use of either a 90° pulse or a 180° pulse. In addition, the slope of the initial decay is higher than that of the 90° pulse. The recoupling signal can be modeled by an exact analytical formula in the ideal case and simulations show that the advantage of the 109.47° pulse is preserved when the quadrupolar coupling constant CQ has a finite value typical of (2)H and (6)Li spins (up to CQ~200kHz). Experimental results on two spin pairs, (2)H-(13)C and (6)Li-(13)C, demonstrate the validity and accuracy of this method.
对于具有小的四极耦合常数的半自旋与四极 S = 1 自旋之间的距离测量，可以使用旋转回波双共振（REDOR）实验来进行。我们推导了一个解析表达式，用于描述对四极自旋施加任意脉冲翻转角后能级之间跃迁的概率，并因此最小化了在脉冲期间各个能级的布居不发生自旋跃迁的概率。结果我们发现，如果四极自旋脉冲的翻转角为 109.47°，最大再耦合值是可能的最大值，并且信号达到最大值 8/9，比使用 90°脉冲或 180°脉冲时更大。此外，初始衰减的斜率高于 90°脉冲的斜率。在理想情况下，再耦合信号可以用一个精确的解析公式来建模，并且模拟表明当四极耦合常数 CQ 具有典型的（2）H 和（6）Li 自旋的有限值（高达 CQ~200kHz）时，109.47°脉冲的优势得以保留。在（2）H -（13）C 和（6）Li -（13）C 这两个自旋对的实验结果证明了该方法的有效性和准确性。
