4. Acquisition

Time requirement: 20 min

Sample a: For step a fill a solid-state rotor with normal water. Be sure that the rotor is completely filled and no air bubbles render the sample inhomogeneous. It often helps to drill a tiny hole in the rotor cap to avoid this situation.
Sample b: For the second step b fill a solid-state rotor with finely powdered adamantane.

Step a: Load standard proton parameters. Do not spin the sample. You have to set:

transmitter power level (1 μs pulse should correspond to a pulse angle of approximately 20°)
td	4 k
sw	125 kHz
o1	2000 Hz to lower frequencies from water signal
p1	1 μs ¹H transmitter pulse
d1	1 s
rg	receiver gain for correct ADC input
ns	1

Using the set-up mode of the spectrometer, where the individual FIDs are not accumulated, display the FID of the water signal, turn the field sweep off, and optimize the various shims of your instrument by measuring the area of the FID. Note that at the magic angle the shim gradients known from high-resolution NMR transform; thus instead of z, z² and z³, you have to use mainly x, xz and xz². If the signal is satisfactory proceed to step b.

Step b: Load the adamantane sample. Turn the spinner to 2500 Hz and load standard ¹³C NMR parameters with high-power continuous-wave decoupling during acquisition. You have to set:

transmitter power level
td	8 k
sw	20 kHz
o1	middle of ¹³C NMR spectrum
o2	middle of ¹H NMR spectrum
p1	4 μs ¹³C transmitter pulse
d1	3 s
decoupler attenuation for high-power cw decoupling
rg	receiver gain for correct ADC input
ns	1

Again, shim on the area of the FID in the set-up mode. Record a spectrum with one transient.