Varian Solid-State NMR - Page 96

6.9 XPOLXMOD1—Waveform Modulated Cross-Polarization
01-999162-00 C0402 VNMR 6.1C User Guide: Solid-State NMR 96
For VNMR 5.1 and later crossp scales the proton waveform and tpwrm scales the X
waveform. The macros xmodramp and xmodcos create their respective .DEC files.
They also serve as a prototype for the creation of custom waveforms.
Parameters
XPOLXMOD1 and XPOLHMOD1make use of the UNITYplus and
UNITY
INOVA
parameters tpwr, tpwrm, dpwr, cppwr, dipolr, crossp, dblvl2, pw and cntct.
See page 85 for a description of these parameters. All other functions (i.e. toss, etc) of
XPOLAR1 are also present.
pattern is a string with the name of the .DEC file used for modulation.
pwpuls is the amplitude of the linear modulator during only the initial proton pulse of
XPOLHMOD1.
crossp is the amplitude of the proton linear modulator during cross polarization and this
value scales the waveform for XPOLHMOD1.
tpwrm is the amplitude of the X linear modulator during cross polarization and this value
scales the waveform for XPOLXMOD1.
Waveforms
Two macros are provided to calculate commonly used waveforms, a cosine function and a
ramp. For general waveforms to be used for cross polarization, a duration of 1.0 in the first
column must be 0.2 microseconds. dmf and dres are not used to control the cross
polarization waveform. You can also set programmed decoupling during acquisition by the
usual procedure using dmf and dres.
xmodcos(frac,per,amp) creates a waveform with the following function:
amp*(1.0 - frac/2.0 + (frac/2.0)*cos(t/per))
where t is time. The resulting .DEC file has the form xmodcos_frac_per_amp.DEC
where frac is x10000 and per is in microseconds. The defaults are per=1/srate (the
value needed for reference 1) and amp=1023.
xmodramp(frac,per,amp) creates a waveform with the following function:
amp*(1.0 - frac/2.0 + (frac/2.0)*(1.0 - 4.0*t/per))
for 0.0 < t < per/2.0
and
amp*(1.0 - frac/2.0 + (frac/2.0)*(-1.0 + 4.0*t/per))
for per/2.0 < t < per
The resulting .DEC file has the form xmodramp_frac_per_amp.DEC where frac is
x10000 and per is in microseconds. The defaults are per=1/srate and amp=1023.
amp is the amplitude of the waveform, amp=1023. VNMR 5.1 and later software provide
scaling of amp with the value of crossp or tpwrm. For earlier versions, set amp to its
fixed value during the pulse sequence (<1023), where amp=1023 is a full amplitude of the
linear modulator.
frac is the fraction of modulated intensity, a value between 0 and 1.0.
per is the period of cosine modulation for 0 to 2
π radians. For a ramp, the slope is negative
(1-4t/per) for t=0 to per/2 and positive (1+4t/per) for t=per/2 to per. Set per
relative to cntct to obtain a specific shape or ramp during the contact time.