NMR-STUDY OF THE T(1) RELAXATION DISPERSION IN THE SMECTIC MESOPHASE OF 4-CHLOROPHENYL 4-UNDECYLOXYBENZOATE

An experimental study of the Larmor frequency dependence of the proton spin-lattice relaxation time [T1(nu(L))] was carried out in the range of nu(L) = 7 to 30 MHz. Two relaxation times describing the evolution of the longitudinal magnetization have been found to have different b ehaviors. One of them has been assigned to the relaxation of the proto ns belonging to the alkyl chain-T1alkyl(nu(L))-. The T1alkyl(nu(L)) di spersion behaves normally without signs of H-1-Cl-35 cross relaxation. The second one, called T(a-c), has a partial contribution from the pr otons bonded to the molecular core and those of the alkyl chain. Well defined H-1-Cl-35 quadrupole dips (QD) have been observed in the T(a-c )(nu) dispersion curve, due to a cross-relaxation process between the core protons and the chlorine nucleus of the molecule. The shape of th e dips are not symmetric, and cannot be fitted by Gaussian or Lorentzi an functions. Computer simulations with asymmetric functions previousl y used in line shape analysis of incommensurate systems and organic gl asses are discussed.