Friday, April 8, 2011
QCPMG for 2H NMR
QCPMG has made a tremendous impact on the field of solid state NMR in that it has enabled the collection of data for very broad resonances for unreceptive nuclei. This technique is based on the collection of a train of echoes, the Fourier transform of which produces a "spikelet" spectrum whose intensity envelope mimics the static line shape. The figure below compares the 2H quadrupolar echo spectrum and the QCPMG spectrum of perdeuterated poly-methyl methacrylate. The spectrum contains two overlapping powder patterns; a narrow one from the rotating methyl groups (QCC ~ 56 kHz) and a much less intense broad one from the rigid methlyene deuterons (QCC ~ 170 kHz). It is clear from the figure that the envelope of spikelets in the QCPMG spectrum reproduces quite well the lineshape in the quadrupolar echo spectrum.