Decoupling and recoupling

One of our aims is to improve the performance of the heteronuclear and homonuclear recoupling experiments at high static magnetic fields and under fast magic-angle spinning (MAS). In fact, fast MAS requires smaller rotors and, thus, smaller sample amount. One option to partially compensate the resulting lower sensitivity is to use more efficient polarization-transfer methods. At the same time, fast MAS enables low-power methods where the nutation frequencies of the rf fields are significantly lower than the MAS frequency. Low-power methods offer the advantage that  the sample heating by the rf irradiation is reduced.

Spin decoupling in solids is a complicated process since several time-dependent processes on different time scales are involved. Firstly, there is the averaging by the radio-frequency field which leads to a partial averaging of the heteronuclear dipolar coupling. Secondly, the strong coupling among the abundant spins leads to spin diffusion resulting in an exchange-type narrowing of the residual line width. Thirdly, MAS introduces an additional time dependence of all anisotropic quantities and leads also to partial or full averaging. Currently the main focus is on developing low-power decoupling methods that achieve line width that are competitive with the ones obtained from high-power decoupling method.

Collaboration with external pageP. K. Madhucall_made (TIFR Mumbai, India) and Anders B. Nielsen (Aarhus University, Denmark).