A generalized Solomon-Bloembergen-Morgan theory for arbitrary electron spin quantum number S: The dipole-dipole coupling between a nuclear spin I = 1/2 and an electron spin system S = 5/2

The modified Solomon-Bloembergen and Morgan theory has been generalized to systems of arbitrary electron spin quantum number and non-extreme narrowing conditions. The effects of multi-exponential electron spin relaxation give rise to a correction term which can generally be derived in closed analytical form. However, only the spectral density at zero electron spin resonance frequency has a noticeable correction value due to multi-exponential electron spin relaxation. For S = 5/2, the maximum value of the correction term for the paramagnetically enhanced nuclear spin-lattice relaxation rate is 5·4% and for nuclear spin-spin relaxation 6·3%. It is therefore likely that the influence of multi-exponential electron spin relaxation on water 1H T 1 NMRD profiles is, within the accuracy of the experimental measurements, difficult to observe.