Proton Relaxation Times in Paramagnetic Solutions. Effects of Electron Spin Relaxation

The proton relaxation time in solutions of paramagnetic ions depends, among other factors, on the relaxation time of the electron spins, τs. It is shown that the latter, for ions of the iron group, is determined mostly by the distortion of the hydrated complex by collisions with other water molecules. The theory provides a quantitative explanation for the decrease in T2 in Mn++ (and other) solutions in very high magnetic fields. The experimentally observed field and temperature dependence of the proton relaxation times, T1 and T2, for ions of the iron group is compared with theory and the features which depend on τs are stressed.