6.8 XPOLWFG1—Cross-Polarization with Programmed Decoupling
01-999162-00 C0402 VNMR 6.1C User Guide: Solid-State NMR
94
XPOLWFG1 gates the waveform generator on and off with a fastline (no AP bus delay) at
the beginning and end of the acquisition period if dm='nny' and dmm='ccp'. If
dm='c' the usual continuous wave decoupling is applied and as usual if dm='n' no
decoupling is applied.
XPOLWFG1 does not include p180, toss, pdp and pcrho at present.
Applicability
XPOLWFG1 is available for UNITYplus and
UNITY
INOVA systems and can be found in
SolidsLib version 2.1.
Macro
The macro xpolwfg1 converts a parameter set, obtained with XPOLAR or XPOLAR1,
for programmed decoupling. Power levels and proton 90
° pulse width are retained. Default
parameters include dseq='tppm2' and dres=90. The value of dmf, the decoupler
modulation frequency, is estimated with the relation dmf= (dipolr/crossp) *(1/
4*pw). This value should be fine-tuned for optimum decoupling.
Parameters
xpolwfg1 uses the UNITYplus parameters, tpwr, tpwrm, dpwr, cppwr, crossp,
db1v12, pw and cntct (see page 85 for a description of these parameters).
dm is set to 'nny' to obtain decoupling.
dmm is set to 'ccp' to obtain programmed decoupling during acquisition and set to 'c'
for continuous decoupling. For dmm='c' the wfg parameters are hidden.
dmf is the decoupler modulation frequency and is set equal to one over four times the
decoupler 90°
° pulse. dmf must be calibrated and depends upon the value of dipolr. The
macro makes an estimate as described above. Calibrate dipolr with a sample of dioxane
and the macro h2cal or to fine tune, obtain spectra versus dmf and choose that with the
greatest narrowing.
dres is the waveform resolution, and it depends on the decoupler waveform.
Waveforms
Three waveforms are included in the shapelib of Solidslib 2.1. For each waveform
name.DEC, set dseq='name'. Set dmf and dres according to the text in each
shapefile.
tppm2.DEC provides phase-modulated decoupling as presented by Bennett et al. For
crystalline materials—for example, glycine and linear polyethylene—PM decoupling
narrows the residual linewidth up to about 30% over CW decoupling. The pattern consists
of approximate
π pulses with alternating phases of about ±10° to 30 degrees°. Vary dmf
and the phase angle in the .DEC file for best decoupling at a particular field strength and
spinning speed.
blew 48.DEC provides decoupling with BLEW-48 according to Burum et. al. BLEW-48
decouples protons from themselves but leaves a scaled
13
C–
1
H dipolar interaction.
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