a pulse program for homonuclear decoupling, adjust the decoupler offset 50 Hz from the CHCl₃ signal, and record spectra with different decoupler attenuations. You have to set:

decoupler attenuation, to be varied
td	4 k
sw	500 Hz
o1	on resonance of ¹H signal
o2	50 Hz towards lower frequency from o1
p1	45° ¹H transmitter pulse
d1	2 s

Measure the displacement of the signal and calculate the decoupler field strength γB₂ [expressed in Hz] from Equation (1)

γB₂ = [2(ν_A − ν₂) (ν_obs − ν_A)]^1/2(1)

where ν_A is the unperturbed resonance frequency, ν₂ the decoupler frequency and ν_obs − ν_A the observed Bloch–Siegert shift. Note that Equation (1) is only valid if the condition of Equation (2) holds.

(γB₂)² ≪ (ν_A − ν₂)².(2)

Repeat the experiment for different decoupler offsets.

5. Processing

Use standard 1D processing as described in Experiment 3.1, and apply zero-filling to ensure enough data points for the relatively small Bloch–Siegert shifts.

6. Result

A typical set of values for ν_A − ν₂ = 50 Hz obtained on an ARX-200 spectrometer is given below, from which the graph was calculated:

Dec. att. [dB]	70	67	64	61	58	55	52	49	46
ν_obs − ν_A [Hz]	0.07	0.12	0.24	0.44	0.79	1.5	3.4	8.7	15.7