
TY  - JOUR
A1  - Pegg, DT 
A1  - Doddrell, DM 
T1  - Frequency dependence of nuclear spin relaxation in paramagnetic transition-metal complexes
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1976
VL  - 29
IS  - 9
SP  - 1885
EP  - 1897
KW  - 
UR  - https://doi.org/10.1071/CH9761885 
N2  - Proton spin-lattice relaxation times have been determined as a function of magnetic field strength (H0) for a series of paramagnetic transition-metal complexes chosen so that, for some, the electron spin relaxation times (te) fall in the Redfield limit (te » tr) while for others te << tr being the rotational correlation time. When te » tr dominates the nuclear relaxation and the experimental results can be readily explained by Redfield theory. When te << tr current theory predicts the nuclear T1 values to get longer as H0 decreases. This is not observed experimentally. This can only be explained by using non-Redfield relaxation theory and by assuming the spacings of the electron-nuclear spin energy levels are not dominated by H0. It is shown that, although the trace of the zero-field splitting tensor is zero     TrD = 0  because TrD is averaged by tr when te < tr the value of Dzz is important in determining the energy-level spacings. By this approach the frequency dependence can be explained. Experimentally, it is shown that a Phase Alternating Pulse Sequence (PAPS) is required to measure T1. The problem originates from interference from transverse magnetization. A density matrix theory of the PAPS sequence is presented. 
ER  -

