Molecular dynamics in smectic A and chiral smectic C phases by deuteron spin relaxation study

Quantitative analyses of deuterium spectral densities of motion for three deuteron sites (ring and C-alpha) at two different Larmor frequencies are reported in the smectic A and C* phases of a partially deuterated smectogen. The motional model is the small step rotational diffusion for reorientations plus internal rotations. In the chiral C* phase, the helical axes are aligned along the external magnetic field and the deuteron spins appear to relax in a macroscopically uniaxial environment. After including the molecular tilt. the reorientation processes in the C* phase were found to have higher activation energies than those in the smectic A phase. (c) 2005 Elsevier B.V. All rights reserved.