6.12 3QMAS1—Triple-Quantum 2D for Quadrupole Nuclei
01-999162-00 C0402 VNMR 6.1C User Guide: Solid-State NMR
100
(DOR) and dynamic angle spinning (DAS). 3QMAS1 is a robust experiment that is well
worth trying before contemplating the use of DOR or DAS.
Macro
The macro s3qmas1 converts a parameter set for the triple-quantum MAS experiment
3QMAS1. pw3q is set to 180
° pulse length (the minimum practical pulse length needed to
excite triple quantum coherence) with the assumption that pw is the 90
° pulse length. If
tpwrm is not present (as in many older parameter sets), 3qmas1 creates it and sets it to
the value of tpwrf. If tpwrf is not present, tpwrm is set to 4095. The default is
pws=0.0 for no refocusing pulse and sw1=sw. The macro s3qmas1 creates the
processing parameter daslp used for shearing (applicable for VNMR 5.2 or greater).
Parameters
3QMAS1 makes use of the
UNITY
INOVA and UNITYplus parameters tpwr, tpwrm, dpwr,
dpwrm and pw. See page 117 for a description of these parameters.
pw is the observe 90
° pulse, in microseconds, for a solution-state sample of the quadrupole
nucleus. The macro s3qmas1 uses pw to calculate the default 180
° pulse. pw is not used
in the pulse-sequence.
pw3q is the length of pulses 1 and 2 of 3QMAS1. It is used to generate triple quantum
coherence (pulse 1) and then return it to single quantum coherence (pulse 2) for detection.
The default is pw3q=2*pw. Set pw3q to a larger value (e.g., pw3q=8*pw) for greater
triple-quantum signal-to-noise in some cases.
tpwr is the observe coarse-attenuator setting for pulses 1 and 2.
tpwrm is the observe linear-modulator setting for pulses 1 and 2.
tpwrs is the observe coarse-attenuator setting for the selective refocusing pulse (pulse 3).
The default is tpwrs=tpwr.
tpwrms is the observe linear-modulator setting for the selective refocusing pulse (pulse 3).
The default is tpwrms=tpwrm/5, but this pulse must be calibrated.
pws is the length of the optional selective refocusing pulse (pulse 3). The default is
pws=0.0 and the refocusing pulse is absent. For refocusing, set pws=10*pw for the
default value of tpwrms=tpwrm/5.
srate must be set to the actual rotor speed. This value is used with periods to calculate
the delay, tau, before the refocusing pulse.
periods is the number of rotor periods before the selective refocusing pulse. This delay
is present only if pws>0.0 and by default it is absent.
daslp is a processing parameter required to shear the triple-quantum 2D dataset and rotate
the narrow axis of each correlation to the f1 dimension. Set daslp<0.0 for I=3/2 and
daslp>0.0 for I=5/2. daslp is available for VNMR version 5.2 and later (refer to the
VNMR Command and Parameter Reference).
phase=1,2 are the sine and cosine components of hypercomplex Fourier transform,
wft2da.
References
Frydman, L.; Harwood, J. S. J. Am. Chem. Soc. 1995, 117, 5367.
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