hard 90º 1H pulse is the most typical starting point in
any homo- and heteronuclear multidimensional NMR experiment basically due
to the sensitivity and relaxation
effects. A 90ºx(1H) pulse converts the pre-equilibrium
longitudinal (Iz) magnetization to transverse magnetization
(-Iy) that usually evolves under the effects of chemical shifts
and/or coupling constants during the following predefined delay. In some
cases, other pulse flip angles can be applied.
The excitation bandwith of a 90º 1H pulse depends of
its duration and, therefore, of the applied power level. In AVANCE spectrometers,
usually short pulses (microseconds) are achieved at maximum power level.
On the other hand, multiplet-selective excitation would require more longer
pulses (milliseconds) at lower power levels.
Easy implementation on AVANCE spectrometers. Pulses are executed
by the pulse program commands p0-p31, which execute a pulse
on the specified channel during the respective duration parameter. p1
and p2 are the 90º and 180º pulses from the observer f1 channel,
respectively. Otherwhise, p3
and p4 are the 90º and 180º pulses from the decoupler
Accurate 90º 1H pulse calibration via transmitter
and/or decoupler is required. For further details about pulse calibrations
in AVANCE spectrometers see Practical
Tutorials: Pulse Calibrations.
The standard way to implement an initial 90º 1H
pulse in a pulse program is
However, in some cases, both power level and channel syntax can be omitted
because they are applied by default from the f1 channel at pl1 power level
When 1H pulses are delivered from the decoupler,
the syntax can be different:
d1 is the relaxation delay (in seconds)
p1 is the 90º 1H pulse (in microseconds) applied
at a power level pl1 from the f1 channel
ph1 is the phase specified at the end of pulse program, and depends of each
A short delay d12 (20 usec) is usually needed to set the pl1
in which the p3 is the 90º 1H
pulse (in microseconds) applied at a power level pl2 from the channel
f2 or decoupler. In this case, the 90º pulse length can be
slightly different compared to the analogous observe pulse. See high-power
90º 1H decouple pulse calibration for more details.
Go to XWINNMR manual,
chapter 184.108.40.206: Acquisition parameters for more info.
See some examples: