Abstract 

Recoupling in MAS NMR by rotorsynchronized pulse sequences,
15th European Experimental NMR Conference, Leipzig, Germany
(Jun. 2000),
talk.
We design rotorsynchronized pulse sequences in MAS NMR by exploiting symmetry theorems, which link the symmetry of the pulse sequences to selection rules for the average Hamiltonian. We have generalized the concept of C7 to sequences denoted CN_{n}^{ν}, consisting of N cycles, with phases incremented in steps of 2πν/N. The entire CN_{n}^{ν} sequence lasts exactly n rotational periods. Using the symmetry C14_{4}^{5}, doublequantum excitation can be obtained at high spinning frequencies (20 kHz). Recently we presented a new class of rotorsynchronized pulse sequences, denoted RN_{n}^{ν}. The sequences consist of N elements each of which rotates the spins by an angle π about the rotating frame xaxis. The phases of the basic elements are alternated by ±πν/N. The sequence of N elements spans exactly n rotational periods. A sequence with the symmetry R14_{2}^{6} can be used to excite doublequantum coherence. A sequence with the symmetry R4_{4}^{1} can be used for zeroquantum recoupling. The CN_{n}^{ν} and RN_{n}^{ν} sequences can be used to irradiate at the Larmor frequencies of several spin species at the same time. We present symmetry theorems for two simultanous RN_{n}^{ν} sequences which allow the construction of rf sequences for recoupling and/or decoupling of certain spin interactions in heteronuclear spin systems. We present solutions for decoupling homonuclear dipolar and CSA interactions while recoupling the heteronuclear dipolar couplings. We use these sequences to excite heteronuclear doublequantum coherence and to obtain heteronuclear twodimensional correlation spectra. 

Dr. Andreas Brinkmann Measurement Science and Standards National Research Council 1200 Montreal Road, M40 Ottawa, Ontario K1A 0R6 Canada Tel. +16139900319 Fax. +16139901555 Andreas.Brinkmann@nrccnrc.gc.ca 

Dr. Andreas Brinkmann, NRCMSS, 1200 Montreal Road, M40,
Ottawa, ON K1A 0R6, Canada Andreas.Brinkmann@nrccnrc.gc.ca 