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Pulse Sequences
Hahn-Echo
The
broad lines typically observed in solids NMR have rapidly decaying free induction
decays which are often incompletely recorded due to a delay for probe ringing.
This delay can lead to a significant part of the FID not being recorded resulting
in not just the loss of signal intensity but spectral distortion as well.
This problem can be overcome with the Hahn-echo pulse sequence which, much
like the solid-echo pulse sequence, refocuses
the transverse magnetization.
Both
experiments were performed with the 3.2 mm MAS probe. With very short rf-pulses
available on the 900 very broad static lineshapes can be correclty recorded.
In
this case a solid-state 90-pulse for 55Mn was 0.6 us.
November,
2005
Quadrupolar
Carr-Purcell Meiboom-Gill (QCPMG) pulse sequence dramatically improves signal-to-noise
in solid-state NMR experiments of quadrupolar nuclei, here for 87Rb (I=3/2).
October,
2005