Selective ¹H decoupling could be used as the relaxation period in NMR experiments starting from a 90º pulse of a low-abundant nucleus, for instance, ¹³C, in order to improve the sensitivity of specific resonances. During this period, a low-power continuous-wave field is applied to achieve selective polarization transfer from the selected ¹H to all near ¹³C via the NOE effect. Such approach should not be advisable for nuclei having negative magnetogyric ratios, for instance, ¹⁵N.

Otherwhise, in the homonuclear case, selective irradiation is used in 1D NOE difference experiments

Easy implementation on AVANCE spectrometers. Selective ¹H decoupling is achieved by defining a low-power irradiation (cw) scheme.

The duration of the ¹H decoupling, d1, will be set to 1-5*T₁(¹³C) (in seconds) and it is very important to define the total experimental time of the NMR experiment to be recorded. In addition , the user only needs to define he power level of the applied cw irradiation (pl26).

The standard way to implement selective ¹H decoupling in a pulse program) is:

... d12 pl26:f2 d11 cw:f2 d1 ... d12 do:f2

in which d11 is the minimum delay for disk I/O (30 msec), d1 is the irradiation (and relaxation) period, pl26 is the power of irradiation, and d12 is the delay needed for power changes (20us). When the decoupling must be stopped, the do:f2 command must be executed.

The overall pre-scan duration will be defined by the addition of all delays existing between the end of the FID acquition (see the go command) and the first pulse creating transverse magnetization.

Some examples: A particular example of this building clock, is the CW irradiation in a on/off-resonance NOEDIFF experiment: Also see Selective 1D Heteronuclear NOE