smlg1015@uxa.cso.uiuc.edu (10/10/89)
I think the ferric salt is added to the water for the following reason:q:
smlg1015@uxa.cso.uiuc.edu (10/10/89)
Adding ferric nitrate to the water makes this experiment one in FMR, ferromagnetic resonance rather than nuclear magnetic resonance. The total electronic spin of iron precesses with a static external magnetic field just as the nuclear spins do. However, the contribution of the iron electronic spin is much greater.
forbes@aries.uiuc.edu (Jeff Forbes) (10/10/89)
Ferric nitrate is a paramagnetic compound (One unpared electron), ferrous nitrate is diamagnetic. The NMR experiment described in "Scientific American" could only detect proton resonances. Proton have the highest resonance frequency in a given field (except for tritium). You could never see iron-57 at the field used in the experiment, its gyromagnetic ratio is too low and its natural abundance is too low. For example, when protons resonate at 360MHz (8.5T), iron-57 resonates at ca. 15MHz. Adding paramagnets to a solution while change the magnetic susceptibility of the solution, which will broaden the line considerably. Some paramagnetic ions will cause a shift in the resonance rather than a broadening, which is usefull for determining the structure of a compound. Paramagnetic ions can also cause the spin system to relax faster, which can be very useful. This discusion would be better in sci.chem than sci.electronics. Jeff Forbes University of Illinois Chemistry Dept.