NMR pulse sequence:
split-t1 MQ-MAS
Split-t1 MQ-MAS
Wimperis and coworkers introduced both amplitude-modulated and phase-modulated split-t1 approaches to MQMAS experiment. In the following, only the phase modulated case is considered.
The t1 evolution period is split between multiple- and single-quantum precession such that the second order quadrupolar broadening is refocused at the end of t1, thereby avoiding the need for shearing.
Shifting the echo by a time tau ensures the collection of the whole echo during the acquisition time and its appearance at a fixed position in the t2 time domain. The third pulse is a selective pi pulse for the central transition.
As with the shifted-echo pulse sequences, the echo amplitude and the antiecho amplitude have opposite signs.
For 3-quantum MAS with phase-modulated split-t1 experiment applied to I = 3/2 system, the anti-echo pathway is involved. Therefore, the anti-echo is recorded.
ACQUISITION: F1-QF
For 3-quantum MAS with phase-modulated split-t1 experiment applied to I = 5/2 system, the echo pathway is involved. Therefore, the echo is recorded.
ACQUISITION: F1-QF
For 5-quantum MAS with phase-modulated split-t1 experiment applied to I = 5/2 system, the anti-echo pathway is involved. Therefore, the anti-echo is recorded.
ACQUISITION: F1-QF