Effect of Molecular Shape on Nuclear Magnetic Relaxation. II. Quadrupole Relaxation

The dependence of quadrupole relaxation in NMR upon molecular shape is examined by regarding the molecule as a rigid ellipsoidal body which shows anisotropic rotational Brownian motions. Dependence of relaxation times upon the angle between the direction of the maximum field gradient and that of the molecular axis is considered also; the complex angular dependence of the relaxation times is derived, which suggests that careful examinations must be taken when we use the information on molecular motion from the other measurements. For example, the effective correlation time obtained from the quadrupole relaxation cannot be used directly to compute the proton relaxation times in an accurate precision.The use of the ordinary theory of anisotropic Brownian motion in molecular system is examined, where the constituents of the ``liquid'' have comparable dimension with that of the solute molecule and they are by no means ``homogeneous.'' The improved theory is applied to the quadrupole relaxation in the system of...