The acquisition of the NMR signal is the last step in any NMR experiment. During this period, the NMR signal is recorded in the time domain as a free-induction decay. When acquire an heteronucleus signal different to ¹H, for instance ¹³C, we have different possiblities. When selective ¹H decoupling is applied, only the information about the corresponding heteronuclear ¹H-C coupling constants are removed.

Other ¹³C acquisition schemes are available:

• Without ¹H-decoupling 
• With ¹H-decoupling 
• With ¹H,Y-decoupling 

Easy implementation on AVANCE spectrometers.

For optimal selective decoupling, the decoupler offset (o2p) and the low-power level (pl26) must be adjusted to an specified resonance.

For more experimental details see Tutorials: Calibration pulses.

The standard way to implement a ¹H acquisition period is:

2 d12 do:f2... (optional) ... d12 pl26:f2 ... go=2 ph31 cw:f2 ... d12 do:f2

in which:

• go starts data acquisition during an acq period using the acquisition parameters previously defined in eda.
• The number after go (=2) defines the loop to be executed. The number of scans (ns) defines the number of times this loop is repeated.
• ph31 is the receiver phase specified at the end of pulse program and must be cycled in accordance to all pulses involved in the pulse sequence.
• The cw:f2 command applies selective ¹H-decoupling from the f2 channel at low-power level pl26 during the acquisition period.
• After the acquisition period, the do:f2 command is necessary to stop the decoupling.