Magnetic Relaxation Dispersion of 7Li:: Interaction with Mn(II) in the aqueous solvent cage

Measurements of Li-7 nuclear spin-lattice relaxation times are made at applied magnetic field strengths from 0.25 mT to 7.05 T, in order to determine directly the form of the frequency dependent spectral densities that modulate relaxation. This Magnetic Relaxation Dispersion (MRD) technique provides detailed information regarding molecular dynamics down to the picosecond time scale. Li-7 MRD measurements on aqueous lithium ion relaxed by the paramagnetic Mn(II) (S = 5/2) ion reveal the formation of a cation-cation complex that has a lifetime at least as long as the rotational correlation time of approximately 100 ps. Translational electron-nuclear dipole-dipole contributions are resolvable, and there is a significant change in the nuclear electric quadrupole contribution to the Li-7 relaxation. The results obtained from solutions of LiCl and LiNO3 are compared and found to be similar.