Zhang S, Gorenstein D G
Sealy Center for Structural Biology, University of Texas Medical Branch, Galveston, Texas, 77555-1157, USA.
J Magn Reson. 2000 Jun;144(2):316-21. doi: 10.1006/jmre.2000.2060.
An analytical solution is given for amplitudes and phases of adiabatic decoupling sidebands as a function of spin inversion time tau. Since all the adiabatic decoupling phases theta(t, tau) refocus at two periods (2T) of the decoupling pulse, the sidebands are located at n/2T rather than at n/T as observed in other decoupling schemes. The real (R(n)(tau)) and imaginary (I(n)(tau)) amplitudes of the sidebands have symmetry R(n)(tau) = R(-n)(tau) and I(n)(tau) = -I(-n)(tau), forming a mirror image between the counterparts of the sidebands. When frequency sweep changes direction all I(n)(tau) are inverted while all R(n)(tau) remain unchanged, leading to pure absorption sidebands with two accumulations as demonstrated by Kupce and Freeman, and to an exchange of sidebands between counterparts. The sum of the real parts for sidebands n = 1 and 2 is almost a constant near on-resonance decoupling, and it increases substantially for large decoupling offsets. The phase defocusing can be minimized for all decoupling offsets by inserting an initial decoupling period with T(ini) = T/2, eliminating all sidebands located at n/2T (n = +/-1, +/-3, +/-5, ...).
给出了绝热去耦边带的幅度和相位作为自旋反转时间τ的函数的解析解。由于所有绝热去耦相位θ(t, τ)在去耦脉冲的两个周期(2T)处重新聚焦，因此边带位于n/2T处，而不是像在其他去耦方案中观察到的那样位于n/T处。边带的实部(R(n)(τ))和虚部(I(n)(τ))具有对称性R(n)(τ)=R(-n)(τ)和I(n)(τ)=-I(-n)(τ)，在边带的对应部分之间形成镜像。当频率扫描改变方向时，所有I(n)(τ)都会反转，而所有R(n)(τ)保持不变，从而产生如Kupce和Freeman所证明的具有两个累积的纯吸收边带，并导致边带在对应部分之间交换。在共振去耦附近，边带n = 1和2的实部之和几乎是一个常数，而对于较大的去耦偏移，它会大幅增加。通过插入一个初始去耦周期T(ini)=T/2，可以使所有去耦偏移的相位散焦最小化，从而消除所有位于n/2T(n = +/-1, +/-3, +/-5, ...)处的边带。
