DETECTION OF 2ND-ORDER DIRECTOR FLUCTUATIONS BY DEUTERON SPIN-SPIN RELAXATION AT A STANDARD HIGH-FIELD

We report on the measurements of deuteron spin-spin relaxation time T- 2 in the nematic phase of MBBA and 5CB using the quadrupolar echo puls e train in a magnetic field of 7 T. The spectral densities J(0)((i))(0 ) at different carbon sites were derived from the T-2 and T-1 measurem ents. Using a model that combined rotational diffusion motion of indiv idual molecules and their internal bond rotations, the spectral densit ies J(1)((i))(omega(0)) and J(2)((i))(2 omega(0)) could be interpreted , while the measured J(0)((i))(0) were too large. It is argued that se cond-order director fluctuations contribute in part to the J(0)((i))(0 ) spectral densities. Thus T-2 measurements at a standard high magneti c field can be used to gain insights on director fluctuations.