THE RHOMBIC EFFECT OF ZERO-FIELD SPLITTING ON THE NUCLEAR-RELAXATION TIMES - QUENCHING OF THE ELECTRON-SPIN ANGULAR-MOMENTUM

The effect of zero-field splitting (ZFS) on the nuclear relaxation rates, T1M-1 and T2M-1, is investigated under the condition that the static ZFS is larger than the energy uncertainty of the ZFS levels. It is shown that the rhombic term E of ZFS drastically reduces the nuclear relaxation rates of a paramagnetic molecule with an integer electron spin quantum number. In this case the nuclear relaxation time is independent of the external magnetic field strength. This signifies quenching of an electron spin angular momentum, which was predicted by N. Bloembergen and L. O. Morgan (J. Chem. Phys. 34, 842, 1961). It is suggested that the true value for the correlation time of lanthanide ion complexes could be much longer than the accepted value, 10-13 s. © 1990.