Static magnetic field, line broadening

Line broadening due to inhomogeneity in the static magnetic field. Ho, as well as in the rf pulse Hj, can contribute to the observed resonance. However, studies of standard sairples, of known natural linewidths, enable the contributions from this source to be determined. In the present case these causes contribute only a few percent, i.e., a few Hz, to the total linewidth and are thus inconsequential to the present problem. Before discussing the different motional contributions to the linewidth. 

The experimental lineshapes of the carboxyl and methyl carbon resonances of fully enriched L-Alanine have been studied in detail at different MAS frequencies and decoupling field strengths. Complex lineshapes at intermediate spinning speeds were explained by the joint effect of off rotational resonance and coherent CSA-dipolar cross-correlation. It was found that coherent CS A-dipolar cross-correlation introduces either a differential intensity and/or a differential broadening of the lines of the J-multiplet. The conditions that lead to such effects were explained and experimentally verified. Additional simulations showed that these effects can be expected over a wide range of static magnetic fields and are not restricted to L-Alanine. 

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