2.3 Shimming

There are several methods for shimming. If you have a Varian built in shim system, you can probably just type acqi to get a pop-up window where you click shim and ajust Z1 and Z2 with the buttons for $\pm$ 1,4,16, and 64, going from fine to coarse to get the maximum lock signal. If you have an integrated spinning system, type spin=20.

If you do not have a built in shim system, i.e. you shim outside of the Vnmr(J) system, you can aquire a single spectrum with broad spectral window (sw=40000 lb=0.5 lsfid=0 ga), set the center far from a signal of interest in your spectrum (a strong signal to be used in shimming) and aquire again (left-click one point out of the region on interest, but not so far from the midle and movetof ga. In the new spectrum do f full dc vsadj to make sure your spectrum is still in the spectral window an not too close to its borders). If it looks weared, do sw=2*sw ga. Then left- and right-click again to select one strong signal in the spectrum. Click in Vnmr^TM or the loop button in VnmrJ^TM to expand this region. Then type d1=1 at=1 pw=3 ga (select a pw value equivalent to a ca. 30 degrees pulse. You can make d1 and at shorter according to the system relaxation). Got again a nice spectrum? Maintain this peak expantion and type gf acqi. You will get a pop-up window. Click to shim with the FID or inside this option click to shim with the spectrum window you have selected. You can use and to fit to window. The reason to make the spectrum a bit out of resonance by moving tof far from a signal of interest is that the pulse itself can interfere in the signal you get here.